I don't know that the coppertone ad is deep enough in our cultural consciousness to be a sound basis for a joke. I feel like most people my age wouldn't get it, I guess older people would. Since Grimmy is a sentient being, wouldn't the presumed pantsing qualify as sexual assault?
Runners-up: Beetle Bailey, Blondie, Garfield, Red and Rover, Rhymes with Orange
Agnes dethrones Get Fuzzy. I'm assuming Agnes is trying to swing some sort of excuse, but she's so spacey, I don't think we can rule out the possibility that she wasn't aware that she was in the hallway. I think it's funnier that way.
Runners-up: Dilbert, Family Circus, Get Fuzzy, Pearls Before Swine