Somebody set you up the bomb.

Hmm, may be a post of yours voted +10 has become community wiki by virtue of being edited too often?

Reputation earned on a post doesn't disappear when it is converted to community wiki.

The only ways I know of to drop 100 reputation quickly are to (1) offer a bounty, which you didn't do, or (2) have one of your posts deleted as spam/offensive. I don't see any questions that have been deleted that way recently, but it's harder to track down answers. If one of your unpopular answers was recently locked and deleted by the community user, this is what happened. I'll have to dig into the database to see if this guess is correct, and to see if there's any funny business with how people are flagging things as spam/offensive.

[Edit: Ryan's comment above identified the offending post]

It does look like the answer François links to above has been downvoted sufficiently that the software has taken it upon itself to mark it as spam. This results in the the post being locked and deleted, with a 100 point penalty.

It's quite unusual for post that isn't hugely obviously spammy to get this many downvotes, but as you can easily observe this particular thread is seeing a huge amount of traffic. I'm afraid I don't have a huge amount of sympathy for getting burnt while playing with fire.

Anixx "answer" is rather off-topic. At the very most, it is a recomendation to take care of one's personal future. Yet the question is rather clearnoy not a request for self-help tips...

Anixx's answer wasn't spam; but if I were one of the people who face losing their jobs I would find it extremely irritating, and probably very offensive, so I can't say that I am unhappy that it got deleted.

@markvs: it's highly doubtful that a university that closes a math department is going to care one bit about a fields medallist or abel prize winner.

Also, because it's irrelevant. The timescale between getting a result, writing it up, submitting it, and having it become a big enough deal in the math community that it brings accolades that the administration can understand is much longer than they have in this situation.

@Anixx: You are wrong. Gregory Perelman was never "about to be fired" from anywhere. He resigned by himself.

Is it wrong that if you have actual prominent results your position in defense will be more strong? This is true not only in mathematics but in every other field.

Anixx, in case you really do not understand what the problem is let me translate how I assume some people (me included) read your suggestion:
"If you were good enough/better, you would not have this problem."
This is rude and useless, and this is an unfortunate combination.

If you did not mean to imply this, then I would say your suggestion is just useless, since to give one of many reasons it is a safe assumption that mathematicians try to obtain as good/interesting results as they can even if they are not faced with imminent termination of their employment. So, that your suggestion is not a suggestion of something one could do (in a planned way).
To be precise (bordering to the ridiculous): the mere assertion that there typically is a positive correlation between the scientific achievements and the chances of (continuation of) emplyoment is true. (Although, in practice even this can be not as clear and direct as one might naively expect.)

So, if you really really made the suggestion in good faith, then yes it was not offensive (in a narrow sense). Did somebody ask you for clarification?

Just imagine your conversation with the boss. He/She says "you do not have enough results..." You can reply either "No, we have results, we advanced such and such field, but you have to be a mathematician to understand it..." or you reply "We have results, we solved one prominent problem which nobody could solve since 1920s. We received such and such prizes for it, our achievements were reported in such and such media and recognized by such and such institutions..."

In other words, you have to present your achievements to your superior not only in the form understandable by him but also in the form which will allow him to cite such achievements when he communicates with his own superiors, colleagues, press and government when he claims more funding for the university from the government etc. Which raises the prestige of the institution. Give a sword in the hands of your university boss and he will never fire you. Even if that sword is not so important in mathematics, but it should be undisputable and concrete.