"You're going to need to stop that," said Peter, shocked out of his reverie enough to realize what was going on. Thoughts of Sirius' previous indiscretion ran through his mind. Well, a Sirius, anyway. He stepped back and wiped at his ear. "It's not funny."
The annoying thing wasn't that it wasn't funny. What was annoying was that it was effective, and his pyjamas offered him no real ability to hide his reaction.