This was actually touched on in Animaniacs and the Sound of Music parody, where Yakko explains that Wakko didn't hit the woman with the mallet because she wasn't being a jerk to them, she was just being nice. The rules apparantly stated that unless a villain threatens, that's when it's time to go all out and annoy the crap out of them. Some of the more wackier cartoons before they started censoring them featured characters back in the 40's that would just start bugging someone for no good reason, but they started to change it over so that they had a valid reason for doing it because the villain was a jerkoff from the start. Screwy Squirrel, and Woody Woodpecker used to do it quite a bit before he became one of the "minding my own business until someone messes with me" character.