Look no further! My insulting limericks will meet all your reasonable (and unreasonable) needs. Simply provide a name and a few key characteristics, and you'll soon have a jaunty rhyme that will leave the recipient crying, with laughter or otherwise.
Please note: these are intended in good fun. While I can't actually control what you do with them, I don't advise or condone sending anonymous insults outside of extreme cases. It can be just as fun to cheer a friend up with with nasty poems about his/her ex than to actually mail them to the ex ;).