I ban smoking classes, characters, and anything else that uses cigarettes, cigars, or pipes that use some sort of tobacco. My pony character on twitter sneezes sticky yellow glitter on smokers.
Just like me in real life! (Seriously: allergies suck, and it's made worse when you're allergic to both incense and cigarettes - while I really don't like the latter, I hate how rude it is to constantly be coughing in someone else's presence just because they've lit up. :/)
I ban OP Nazis. They wait till someone posts something interesting and possibly useful but only tangentially related to the original topic. Then they object, despite not being the OP, the original discussion being completed, no one had posted anything for several months, and their post adding nothing.