Every office has one; the guy who saves every note, every email, every IM that he might be able to use to cover his ass and deflect blame, sometimes directly your way. You might be interested in a new, free tool from Big String, then -- self-destructing instant messages.
The program, available as a plug-in with most IM programs including AOL's, will automatically destroy messages after an interval you determine. The company claims that these messages also can't be printed, scraped, forewarded, stored, or captured with a screenshot.
Big String does, however, cooperate with law enforcement, so that the misdeeds of stalkers and other miscreants can be recovered by the Man.
If you're the type of person that types before you think and find yourself wishing to undo distemperate messages, you might give Big String a try. It won't undo your kvetch, but it might keep your message from going viral.
Kill your IM faux pas