Taylor Swift to Calvin Harris: I'm Bouncing ... But I Suck At It

Taylor Swift's famously long legs ain't made for bouncing ... 'cause you gotta see her epic belly flop.

Swiftee and her bf Calvin Harris are off on some tropical island celebrating their first anniversary, and she decided to show off on one of those giant water trampolines.

The best part? Calvin laughing his ass off at her. Coolest guy.