SLUC

An abbriviation for "someone likes using caps" used in a chatroom/instant messenger when someone is acting obnoxious by typing all/most of his/her messages in capital letters:

ILikePie324: HA HA THAT'S SO FUNNY
ILikePie324: IT'S SO GREAT TO HEAR FROM ALL OF YOU AGAIN!
AwesomeDude666: SLUC... God, you're being annoying...
ILikePie324: HUH?!!!!1
AwesomeDude666: http://www.urbandictionary.com look it up