JENNIFER ANISTON has a new ad for SmartWater on YouTube.  The whole thing is a joke about viral advertising, and includes some Internet 'classics' like dancing babies and Double Rainbow Guy.

And at one point, she kicks a guy in the crotch, and explains it'll get the video another "100,000 hits." Then at the end, she asks what the title of the video is, and a guy tells her they're calling it "Jennifer Aniston's Sex Tape"...

(For what it's worth... I think Brad Pitt is an idiot... thank you!)