If you're going to take a jab at someone, you should at least have a bit more of a personal relationship with them. I feel like you can be funny and clever, as opposed to just outright vile.
In 'There's Something About Mary' and 'Dumb & Dumber,' I ended up improvising quite a bit of my scenes, and later I didn't even remember what I'd said because I just winged it. When I went and saw the movie, I was as stunned as everyone else was.