Ignore the salt 'n' pepper hair and the penchants for making serious movies and trying to save the world on his downtime. At heart, George Clooney is still a big kid. Just ask any of the victims of his many pranks.

Clooney is one of Hollywood's most notorious jokesters, and his marks are a reading list of the town's hottest stars. And these aren't you're average Saran Wrap-on-the-toilet-seat type of hijinks, mind you -- Clooney goes all out and he's in it for the long con. By comparison, Ashton Kutcher's "Punk'd" is, well, child's play.

Here are some of the "American" star's best pranks, so we've heard…

The Bumper Sticker

It was a case of good icy revenge for Clooney after falling victim to one of Brad Pitt's pranks on the set of "Ocean's Twelve." Pitt had sent a memo to the crew suggesting that Clooney had insisted on being referred to by his character name (Danny). Clooney's response was to bumper sticker Pitt's car. The first read, "I'm gay and I vote." The second was even more incendiary. It read, "Small Penis on Board." Ouch. "People were honking at him and waving," explained co-star Matt Damon. "And he thinks it's because he's Brad Pitt and he's waving back."

The Artist

One of Clooney's more elaborate pranks involved a canvas painting he gifted to best pal and actor Richard Kind. "I remember finding a painting that someone had thrown away," explained Clooney. "It was out by the garbage and I drove by it a few times. It was this gigantic, awful painting. I finally stopped and picked it up and took it home and signed my name to it and framed it. And for about a year, my buddy Richard would go, 'Hey, you want to play golf?' And I'd go, 'I can't. I've got art class.' And then on his 40th birthday I said, 'My art teacher's really proud of me but this (painting) is the first one we're both really proud of. You've been so supportive, I want you to have it.' It hung over his couch for another two years and everyone knew except for him."

The Candy Man

A boozy flight to LA was the scene of a particularly devious prank by Clooney and Pitt. The pair challenged producer Jerry Weintraub to a drinking game but were careful to fill their glasses with water. When Weintraub passed out, drunk, the pair filled his underwear with M&Ms. "When I got up I felt squishy stuff in my shoes, in my underwear, in my clothes, and they put M&M's in my underwear," laughed Weintraub. "I said, 'You sons of b***hes! What did you guys do to me?' I found out from the pilots and the stewardess they were drinking water."

The Appearance

It was all fun and games on the set of "Ocean's Twelve" it seems, because Clooney didn't stop at bumper stickers to get Pitt back for his antics. While the actors were staying at an Italian hotel, Clooney whipped up the throng of waiting fans in order to torment Pitt. The star appeared on Pitt's balcony and sent the crowd wild. "For the rest of the night Brad had teenagers chanting, 'George, George!' at his window," Clooney bragged.

The Pants Trick

When Matt Damon pranked Clooney by telling a reporter that the "ER" alum was definitely gay, Clooney got his own back. When Damon stayed at Clooney's Italian villa, and was trying to lose weight for a role, Clooney hired a tailor to take in Damon's pants at the waist each day during his stay. "He couldn't understand how he seemed to be gaining weight while he was trying so hard to lose it," laughed Clooney.

The Pap-Swatter

The star once pranked the paparazzi by pretending to host the wedding of Brad Pitt and Angelina Jolie. "You would never go to Lake Como in February," he told the "Today Show." "It's sort of rainy. You certainly wouldn't have an outdoor wedding. But once the story started, and all these people started showing up – and I mean hundreds and hundreds of press people outside the house, including people from all the entertainment shows. I called and ordered high-top tables and had them put out on the front lawn because helicopters are flying over. It went on for two weeks -- people thinking there was going to be a wedding."

The Crude

Perhaps Clooney's most outrageous prank involved making sure he never got hold of your camera. The star used to steal friends' cameras and then snap a photo of his private parts wearing a pair of glasses. "We called him Mr. Face," he told Esquire. "You put sunglasses and a cigarette, and it actually looks like a person. I haven't done that in a long time. I think 1988 was my last Mr. Face impersonation. My cousin Miguel [Ferrer] and I did it to Pat Boone's camera once. He actually had a good sense of humor about it."

The Dad-Botherer

Of all the Hollywood stars not to mess with, Bruce Willis would be on top of many people's lists. Not for Clooney, who pranked the "Die Hard" star at a party by engaging him in conversation about the young men who'd been making eyes at Willis' daughter Rumer. The jig was up when he tried to bring Rumer in on the joke. She went up to her father and said, "Dad, George told me to tell you that – uh, I forget his name – was talking to me."

The Long Con

It never ends for the star, who told "Extra" back in January he was in it for the long haul after Pitt and Damon pranked Clooney by having a male stripper profess his undying love for the star at a recent press conference. "I've been working on [getting them back]," he said. "In fact, I'm in the middle of it right now. This is how it works, you know, it might take years."