A belt dick is the part of the belt that sticks out after it is fastened around ones waist. It is often because the belt is too short to reach the beltloop, therefore, you end up with a belt dick hard on.
omg she must have gained ten pounds over the weekend. her belt is too short and now she has a belt dick hard on. usually accompanied by slight to severe muffin top
A sexual prosthesis used by men or women usually homo couples.
Go get my belt dick so I can get in that ass