Bum Tussle
To use one's bum to assert your position in bed. A back to back Fight, a struggle for an optimum sleeping position.
You and your wife are sharing a bed, bum to bum.. she has more than you. A Bum Tussle insues! You win!! HOrrrayy, you are the Bum Tussle Champion. Enjoy the extra space in bed and a full nights rest, looks like your wife will wake up cranky, sucks to be her.