Moulstoning is the act of joining in on a joke which is about yourself and in turn, ruining the joke, making it not funny and making it totally lame.
Nick: You are ugly
Harry: Well, soooorry guys my hair straightener was broken and I didn't put on make-up (trying to be funny)
Nick: OH MY GOD!! You're moulstoning
Harry: Well, soooorry guys my hair straightener was broken and I didn't put on make-up (trying to be funny)
Nick: OH MY GOD!! You're moulstoning
by Roger McCallum November 11, 2011