A bubble butt
A bubble butt is not a huge butt. It's a tight little round butt that looks like it could pop any second. It's like a donut made for a skinny person.
My cousin's butt looks like a bubblegum bubble. I want to pop it.
That girl walks in and her butt looks like it’s about to burst.
I swear her butt is so round it’s a crime.