Girl: "She has to guess how many months have 31 days."
Guy: (counting knuckles) "It's eight."
Girl: "No, it's seven."
Guy: (counting knuckles again) "No. It's eight. January, March, May, July, August, October, December. Five knuckles plus three knuckles is eight."
Girl: "Yeah, that's great. Except you only have four knuckles on your hand, dumbass."
-- Submitted by Power