Ass-thumbing is when you go to the bar and drink Captain and ginger, and then you strategically place your yourself between 2 people and nonchalantly stick your thumb in someone's butt. The goal is not to get caught and to make the person getting ass-thumbed think it was someone else. Ass-thumbing also goes by " doing the Crosby" Ass- thumbing is believed to be a German tradition, and in the States, there is an ass-thumbing group in the mid coast Maine area.
by Aaron goodwin July 06, 2014