B.T.S.B.S.
A slang term for girls who wear tight shirts and their bellies pop out like a balloon. It means Bellies That Should Be Popped.
She’s wearing a shirt so tight it’s like her belly is about to burst. B. T. S. B. S. is a thing.
That shirt is so tight it looks like her belly is trying to escape. B. T. S. B. S. is real.
Why is she wearing that shirt? Her belly looks like it wants to be free. B. T. S. B. S. is the only explanation.