Any lingering doubts that Gerard Butler is just a hormonal teenager trapped in a grown man's body were erased on Saturday night in Paris.

That's when TMZ caught him making an ungentlemanly hand gesture on Jennifer Aniston's super-toned tuchus as they posed for pics on a cruise of the Seine during the European promotional tour for "The Bounty Hunter."

Unfortunately, it doesn't appear that the actress responded to the Scottish star's devil-horned digital liberties with a hard slap to his scruffy mug. Is that a sign that she didn't mind his immature lewdness, or is she too polite and ladylike to make a scene in public? Your guess is as good as ours.

RELATED VIDEO: See Jen and Gerard cruising the Seine

As luck (and a well-oiled PR machine) would have it, People magazine has all the details of the "private" cruise.

A source says the co-stars, who have brushed off long-simmering romance rumblings ad nauseam, were looking "friendly and flirty" while "hugging and touching each other" on the sumptuous yacht.

RELATED: Jen and Gerard's steamy W spread

"They were very close," relays the spy. "They really warmed up the room."

That room, in case you were wondering, was filled with about 20 other people, who apparently took careful notes on what Jen and Gerry ate and drank (salad and chicken for her; lobster for him; berries and champagne for dessert).

RELATED: Jen's Mexican B-Day Getaway With Gerard

The pair isn't unfamiliar with public snuggle-bunnies: They've hammed up their handsiness on the red carpet for months, including Sunday's Paris premiere of their critically eviscerated flick.

Speaking of bad reviews, the salmon-pink ruffled gown Jen stepped out in didn't exactly earn raves, although we're just so happy to see her in a bright color that we're willing to overlook the side-view fabric bloating issue. We'll also refrain from wading into the debate over whether she knew the diamond earrings she was sporting looked exactly like the ones Angelina Jolie wore to the "Beyond Borders" premiere in 2003.

RELATED: See more photos of Jen

By the by, Aniston might need a new publicity move next time she's in Paris. Seems she's something of an expert when it comes to dining along the Seine with a male companion.

She took the same romantic trip with Vince Vaughn to quiet rift rumors while stumping for "The Break-Up" in 2006. Two years earlier, she enjoyed the cruise with Brad Pitt. They split eight months later.

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