It is said (by my friend AT) that Larry Barker (former ECD of BMP, and prior to that, WCRS) had only three rules for his Creatives: no chameleons, no mime artists, and no ginger-haired people.
Apparently a team once walked into his office and he blew out their ad before they had even showed it to him, because he could see through the paper that it was a chameleon.
Mind you, this story is a few years old. Maybe the Top 3 Ad Cliches of today would be different. What would you nominate?