I hate it when things that are totally funny lose their charm due to people constantly repeating them. The worst example of this is The Family Guy, post-dvd release. It seems like everywhere I go there is some jackass quoting the Family Guy (usually incorrectly). It's gotten to the point that I don't even find the Peter stubbing his shin scene funny anymore (because that's the one people seem to quote the most).
Another recent example is the Lil' Jon skit on the Chappelle show. Once very funny, no longer can stand it.
Oh well.
Any other examples?