A halfing moment refers to an incredibly failed attempt trying to be funny, humorous, comical or amusing in any type of way. It's usually executed by a person desperate for acceptance and approval of their unexisting personality, of which they hopelessly can't getchange.
person 1: bro why you shoot that baby!
person 2 : are you being racist man is this because im white.
person 1: you are being such a keemstar moment dude.