Spam. There's a word that, due to the wonders of technology, I now have a new definition of. Spam being delicious, and funny/pointless/annoying.

Gay. There's another one, though not due to the internet. Probably due to video games or something...I dunno, ask my nan.

I'm curious as to why definitions of words suddenly(ish) change. How do people just decide that one word means something different all of a sudden? How, damnit, HOW???