Ass buckling
When you tighten your ass to the point where you feel immense pain.
Did you hear Gabe’s ass buckling last night?
Ass buckle
An "ass job", where a guy fucks a girls ass cheeks, without penetration, and in order to increase friction the girl will lower her belt down around her ass to squeeze her ass cheeks together to make it more pleasurable.
She put on the ass buckle for me and I was done!