Naked Dingus
A guy takes off his pants, crouches, and punches his butt with a fist like it’s a butt-shaped punching bag. People do this to mock each other or to get a laugh from a group.
At the beach, my friend did the Naked Dingus in front of a group of kids. I joined in and we both got laughed at.
During a sleepover, my brother did the Naked Dingus to tease me. I did it back and we both had a laugh.
At the movie theater, my friend did the Naked Dingus in front of the whole theater. I was so shocked I fell out of my seat.