Definitions by Taco Monkey

one-and-a-halfsome 

Secks between a normal-sized person and a midget.

A twosome would involve two normal-sized people, so therefore a one-and-a-halfsome would involve a normal-sized person and a person half the size of a normal person, or a midget.

one-and-a-halfsome by Taco Monkey January 2, 2007