I was shocked to see the four-letter word in the first comment to this question, by the answering person himself. Why do we tolerate such language? I thought this was a site for mathematics professionals, not a children's playground or a sailor's club. (The conversation in the comments also suggests an attempt at gaming the reputation system.)

A bit of history: I flagged the comment for moderator attention, shortly afterward the answer disappeared, but it has reappeared since, with the comment intact. I also don't understand the upvotes: are these genuine signs of support or instances of people misclicking while trying to flag it?

+1 Mariano. I agree, it doesn't bother me one bit to see the word 'fuck' ones in a while, I mean we're all adults here right? In my opinion the next comment by that user is much more borderline. It reads "hey, accept my answer, old time's sake."

I certainly find the language distasteful. I'd not be opposed to banning it if we started seeing a lot of it, but I don't know if a formal policy is needed at this point.

When I saw VP's moderator flag, the answer had been deleted by the owner, so I didn't do anything about it, not realizing that it might be undeleted later. If the answer hadn't been deleted, I think I would have deleted it (the comment, not the answer) and sent an email to the comment owner. While I don't think we should have any hard rules about language, my overarching philosophy is that people should treat MO like a large seminar. You don't have to be uptight to attend a seminar, but you are expected to exhibit a certain minimum level of professionalism. You (almost?) don't ever swear to get your point across in a paper or a talk; I don't see why you should ever need to swear on MO. It seems like there is real potential cost to people swearing on MO, but I can't think of any real benefit to it.

@Noah: The difference is that if someone says "fuck" at tea, it's because they know exactly who they're speaking with. I would be pretty surprised if someone was casually swearing at tea regardless of who was standing around listening.

"Also, are you aware that this specific word is considered demeaning to women?"

No, definitely not aware. Please explain?

"The fact that we are all adults"...---apart from the fact that my 8-year-old often reads MO over my shoulder. @Jeremy: you're puzzled why anyone cares. People swear in the street. I don't think twice when I hear people swear in the street when I'm walking to work alone. But I get upset when I hear people swear in the street when I'm walking with my kids. When I was in my 20s I wouldn't think twice about swearing in the street in a conversation with friends, and who cares if anyone else is listening---it's not their business. Now I have kids I never swear in public, even when my kids aren't around. Perhaps it's called getting older. But my point is that it's not just about what you think---it's about what everyone around you thinks too and you have to take on board the fact that some people might think differently. That's why people care about this.

I'm the one who said "fuck". Here's my take: I know that our culture has decided that "fuck" is an offensive word, and so yes, I knew I would be offending some people here by using it. But I don't think there's any good reason for "fuck" to be offensive other than cultural inertia, so I try not to contribute to its suppression. Apologies for any umbrage, but consider its use as a plea to get over it and worry about something -- anything -- important.

To (mis)quote George Carlin, There are no good or bad words. It's the context that makes them good or bad.

@Anton: I guess you haven't spent as much time at tea with Ben or Jen as I have. You're right that people don't swear in large seminars, but at Berkeley I'm pretty sure I've heard people swear in small seminars.

But anyway, I wouldn't swear on MO for exactly the reason that you don't know who's reading and I wouldn't want people to think badly of me over something unimportant. But for this reason I think the best response is not a censorship policy but instead a comment complaining which people can vote up. When people see that lots of people are bothered then I'd expect them to change their behavior, while censorship may have the opposite effect.

In any case, it looks like the comment is gone.

@Dustin : I don't think a desire to "shock the prudes" is a sufficient reason to lower the level of civility on MO. Most people grow out of this desire by the time they leave their teenage years...

@Daniel : The answer had very little to do with the origin of the name "perverse sheaf". My feeling is that it was entirely off-topic.

@Daniel : But Grothendieck didn't invent the name perverse sheaf. And bracketing that, the only "deeper truth" that Dustin's answer tells about concerns Dustin himself, which is not on-topic for MO.

@Andy: It seems to me that "accepting" an answer to a soft question such as this is a purely subjective decision; I interpret my question in one way, and you may interpret it in another. That said, my interpretation does have the advantage of (tautologically) being the one under which I intended the question to be understood.

Just for clarity's sake, I'll spell out my interpretation of the question I asked: Why call such well-behaved objects "perverse"? (If they were clearly pathological, I would not have asked the question in the first place, since the answer would be obvious.) None of the other answers even attempted to address this concern, really. While Dustin's answer is certainly speculation, it does address the question in the sense I intended it.

And don't you think there's something mysterious about Grothendieck's claim that: "It is evident that of all the ‘things’ in the universe, we humans are the only ones to whom this term ['perverse'] could ever apply."?

@Dustin: Now that I know that your comment was joyous and full of tenderness, I am both flattered and uncomfortable.

Kevin Buzzard said:

Now I have kids I never swear in public, even when my kids aren't around. Perhaps it's called getting older. But my point is that it's not just about what you think---it's about what everyone around you thinks too and you have to take on board the fact that some people might think differently. That's why people care about this.

Andy Putman said:

@Dustin : I don't think a desire to "shock the prudes" is a sufficient reason to lower the level of civility on MO. Most people grow out of this desire by the time they leave their teenage years...

+100 each. It's all about levels/modes of discourse, surely? I don't take any offence when one of my friends and colleagues swears liberally as emotional punctuation in discussing maths or the business of maths, whether over coffee or beer -- as I do, and as many of us probably do to varying extents. That isn't a reason to do it on MO, because as Kevin says there are people who find it inappropriate, and it is hardly a great effort not to swear while writing an answer, surely?

(See also my old grousing that MO is not a pub. Speaking as someone who likes maths, and likes pubs.)

@Daniel Litt : Your question explicitly asked for the 'etymology of the term "perverse sheaf"'. As such, it was a fine question. If I had known that you were looking for a pseudo-philosophical discussion of the use of the word perverse, then I would have voted to close the question as "subjective and argumentative". And I generally don't have a problem with discussion questions -- I just like them to be about math.

@Andy Putnam: It's probably not quite fair to say that the question 'Why call such well-behaved objects "perverse"?' (which is clearly a subquestion of "What is the etymology of the term "perverse sheaf"?") calls for a "pseudo-philosophical discussion of the use of the word perverse." Certainly any answer to the general etymological question should address the reasons for using the word "perverse," if there are any. It seems likely to me that the subquestion is of interest to at least some mathematicians, despite being aesthetic.

On a more pleasant note, I just remembered that I recently ran across your preprint "Obtaining presentations from group actions without making choices" while googling for something or other, and I enjoyed it a great deal.

By the way, while I'm relatively new to MO, I feel like this thread is getting a bit more personal than I would have expected. So as a gesture of friendliness, I'll let you have the last word in this exchange.

@Dustin: While I obviously have no objection to swearing, the fact that other users do is probably a good reason not to do so, regardless of what their reasons are for objecting, as Yemon Choi points out. (Feel free to swear via email, however.)

I actually agree with Andy about double entendres.

Dustin, it's not only inappropriate and rude to make sexual comments in a professional environment, it's also often illegal. You're making a fool of yourself in public right now and for your own sake you should stop.

Noah, let those who think I'm a fool think I'm a fool.

Andy, and I'm being sincere here, I do appreciate the advise you just gave, and thank you very much for your concern. But I have given thought to and am satisfied with the image that I'm projecting of myself. I just please wish you'd take my points.

I second Daniel's call for deletions. I don't want Dustin's immature and inappropriate comments making MO look bad to people who run across this thread through google.

I call for it to stay; who exactly is embarrassed about the image of themselves that has been broadcast in this thread?

Daniel, I happily will, with apologies. Consider my previous message retracted.

@Dustin and Andy Putnam: Thank you both. Hopefully moderators will accede to what now seems to be a request from all the principals of this thread.

I'm closing this thread now. Rather than deleting the whole thread, I was thinking of simply deleting all the comments below a certain point (I'm not sure exactly what point). If you have an opinion about this, email moderators@mathoverflow.net.

Tangentially related, there's a new section of the FAQ: Where's the rule that says I have to wear pants?.

Update: At least one person has emailed objecting to any moderator deletions in this thread. I may be wrong, but I don't really see much harm in leaving the thread up. Aside from Dustin making himself out to be a troll (perhaps unintentionally), I don't think anybody embarrassed themselves. If you want me to delete or edit any of your own comments, email me directly and I'll happily do it.