Thumb Butted

When you stick your thumb in a girls butt during sex. You've gotta love it like it's your last.

Person 1: Yooo how was your night?? Did that girl sleep over?
Person 2: Ya lmao I thumb butted I think I love her.

Thumb-butting

When you are hitting it from behind and have your thumb in her butt at the same time. Thumb-butting it.

She seemed like she wanted it so to test the waters I was thumb-butting it.