BOYS WILL BE BOYS DEPT.:

Even GEORGE CLOONEY and BRAD PITT’s man-crush pales beside the budding bro-mance between “21 Jump Street” stars CHANNING TATUM and JONAH HILL – who often teased each other on the movie set by…Eeeewwww!...twisting each other’s nipples!

Ripped hunk Tatum kicked off the booby-bullying, reports My Jump Street Spy, constantly tweaking Jonah’s chest petals – while Jonah’s attempts to retaliate were mostly…er, nipped in the bud!

“Getting back at Channing was impossible,” said the source.

“Jonah just couldn’t get any leverage on those nipples of his – because it’s all muscle under there.”

Ow, ow…OOUCH!