Attention Tara Reid — we now interrupt your Mexican vacay for shots of your BF caressing a tremendous bikini-clad ass … that is NOT yours!

Not that Tara needed us to tell her, but yeah … her dude, Yavuz Cansiz, shared a nice tight embrace with a female friend in Cancun while Tara got a bird’s-eye view of the action.

As you’d expect, Yavuz had some ‘splaining to do.

The last time Tara had this look on her face … Kim Kardashian and Paris Hilton’s asses were cruising by her.