To hork or lodge the erect thumb straight into the anus of a woman. "also know as lil butt thumb"
Sam M like to butt thumb anna chew
Butt thumbing is much like butt fingering, except that the thumb is used. It tends to be more intense because of the dexteral advantage of the thumb over fingers for two main reasons:
1. The thumb does not have other fingers getting in its way
2. It is much sassier
starting now, every chick i bone is gonna experience the butt thumb too