What are the weirdest computer bugs you have ever come across?

A friend of mine's Windows would work ok, but if she opened up her media player, the text in all programs would get screwy, letters would have huge gaps between them. After looking around a lot, I thought about scandisk (or was it chkdsk?). It identified some bad sectors where a font file was residing on disk.

Why did it only go screwy when she opened her media player? She had songs with Mandarin Chinese titles. Only when Windows tried to load the non-Latin characters from the font did it hit the bad sector(s).

My favorites are the class of bugs caused by the phase of the moon: http://catb.org/jargon/html/P/phase-of-the-moon.html

One of the very early versions of Word Perfect. I was typing some word that had "lm" in the middle of it (I don't remember which word it was). So I typed an "l", and that was fine. Then I typed an "m", and got another "l". I noticed this immediately - before I let up the "m" key. So I held it down, and I got a string of "l"s. I let it up, and all the "l"s (except the first one) turned into "m"s.

I promise that I was stone-cold sober when this happened, and I do not hallucinate (so far as I know).

accepted "(char *)" in microport unix compiler, back in the day. correct was "(char *)0". lint missed the error, as well.

you youngsters have no idea you good you have it.