Very rarely have I felt the need to get revenge, HOWEVER....
When my ex left me with a newborn baby and moved in with a "friend" of ours (I was also 22, so I'm going to use that as an excuse for what I did

) I had a little fun.
He was a big guy - 6'2" 200 pounds back then and while I was still short, I was about 40 pounds lighter than I am now. For some reason, one night we were trashed and he had on his coke bottle glasses (was blind as bat - which my son has inherited) and put on a headband of mine, my leopard skin panties and a black bra. And I took a picture. Big mistake on his part.
I took the picture and made "LOST" posters out of it. I put on there his name, telephone number, where he was living, etc. and noted that he'd left me with a baby and no money. Then I plastered them all around where he lived - phone poles, apartment clubhouse, grocery stores, etc. We knew A LOT of people around there as she lived in the same complex we lived in before we bought the house so a lot of his friends saw it.
Then there was the time a few weeks later I sold all his stuff at a garage sale..........
But he's really the only person who's pissed me off enough to do that sort of crap.
