If you feel inspired to pull a fast one on your buddy, you could always go the classic route of drawing penises on his face with a Sharpie when he's asleep. That way, you can only be charged with being a bad friend. But tattooing a fifteen-inch penis onto his back when you've told him that you're tattooing a yin-yang symbol? That'll earn you two counts of assault.
Or at least that was the case for the cavalier Australian who did exactly that to his unwitting friend, who didn't realize what had happened until he got home. "I don't think it's the tattoo you were after," his roommate told him, in the understatement of the year.
The 40-cm penis tattoo apparently also came with a slogan that questioned that tattooed man's sexual orientation. All in all, it'll cost the guy up to $2000 to have lasers erase the unfortunate prank tattoo.
And that's why you should never go to Australia.