Apparition Accident
It was Harry's sixth year, and he was in the great Hall with his fellow year mates, listening to the Mr. Twycross from the Ministry, who was teaching them to apparate.
"Destination, Deliberation and Determination" said Mr. Twycross.
Harry translated that to mean, concentrate on where you are going, what you want to move there, and then do it.
Harry then concentrated hard on moving himself, his body and his magic into the hoop in front of him, his magic responded to his desire and as he twisted he disappeared and reappeared in the hoop.
Two things were immediately apparent. The first was that he forgot to include his clothes in his desire, so he appeared naked. The second was that he wanted to move himself and his magic. He was unaware that his scar contained a piece of someone else, so that was left behind.
As the students around him gasped at the very naked Harry Potter in their midst, a piece of skin shaped like his famous scar fell to the ground behind him and started screaming as it shrivelled.
AN
As you must realise by now, I come up with some weird ideas!