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Jennifer Lopez is kissing and telling ... and it's not the best news if your name is George Clooney!

While appearing on "The Daily Show," J.Lo was asked ... goaded, actually ... by Jon Stewart about being forced on camera to kiss bad kissers. He said he had a sneaking suspicion that George was the worst kisser of J. Lo's past co-stars, from when the two starred in 1998's "Out of Sight."

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"He was OK," Jen giggled. "He was all right."

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Say what you will, but Jen knows a things or two about kissing in movies. She said, "I've done over 30 movies, so the ratio ... some are good, some are not so good."

She did add that none of her past co-stars had bad breath, thankfully.

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Jennifer is now starring in "The Boy Next Door," where she -- you guessed it -- has several kissing scenes with co-star Ryan Guzman.

See, we told you, she may actually be a formidable judge on all things regarding the mouth -- on "American Idol" or otherwise.