The Boy with the Dragon Tattoo
It was a well established rumour within Gryffindor house that following the Triwizard Tournament, Harry Potter had adorned himself with a large dragon tattoo.
Admittedly the Weasley twins had started the rumour, so it really wasn't much to go on, but in the heart of every female Hogwarts student was the hope that beneath his dark robes, Harry's back was ablaze with ink. And that one day they might see it.
Ron, of course, was the first to dispel these rumours, pointing out that he had seen Harry's bare back lots of times, and with the exception f the odd mole, there was nothing on it.
Naturally the twins had a field day with this – "Was ickle Ronnikins checking out the Great Harry Potter?" – which while it sent Ron red to the ears, didn't seem to bother Harry all too much. He might never have had a brother, but he understood that homosexual teasing was pretty much par for the course. No wonder Ron was so desperate to get with Hermione.
Speaking of Hermione, she was one of two people who weren't buying into the rumour – saying stuff like "Harry wouldn't be so stupid as to permanently mark his body with ink" and "Harry, you need to find fangirls with an IQ higher than that of the Giant Squid." Harry was beginning to appreciate what having a mother must be like.
The other person who did not believe Harry sported a giant dragon tattoo on his back was Draco Malfoy. Not that he was likely to admit out loud the reason for this.
That reason being that he had had many occasion to examine Harry's skin, and with the exception of a few bite marks (which Malfoy wasn't openly admitting to either) Harry's back was ink free.
There was a dragon tattoo on Harry's left arse cheek though.
Malfoy had put it there himself.