A term used in response (typically to notify a friend) when a lurk or unwanted person says something useless, unwanted, or totally nonconstructive to the occasion or conversation. Also used to avoid calling the person out for saying something utterly retarded.
Sounds like the squealing of a pig.
Alex: So what did you think about Mary?
Dylan: She was pretty hot. We were hookin up in one of the spare rooms for about an hour during the party.
Some Lurk: Ya I saw her standing outside by the pool for a while.
Dylan @Alex: Raint!