bum pinch 

A light squeeze to someone's ass cheek to show appreciation for the shape of that person's posterior. One must carefully select the proper social situation for a bum pinch, since sometimes it can be considered socially inappropriate.

A cute dancer at the strip club deliberately put her sweet ass in my face, so I gave her a little bum pinch to show my appreciation.

bum pinch by Chad Apollo August 2, 2019