According to the gossip at the Slytherin breakfast table, someone transfigured a snake into a tape measure and sent it after Ron as a prank while he was in the bath and he came out screaming and stark naked because the thing was trying to crawl -- um.

Then I heard from Lavender Brown it wasn't actually a transfigured snake, just a tailor's tape measure, and Ginevra gave it to him but didn't warn him about ALL the measurements it might try to get. Lav thought Ginevra might have done it on purpose to be cruel, I think she just didn't think about it.