This is a derogatory term usually referring to individuals who are ; dumb, lame, slow, fat, slimey, gay, jewish, black, ugly, goonish, grimey, smelly, scrawny, weak, and just down right uncool.
This term is also synonymous with the term dehoff
Guy 1: "dude that snail clown's trying to piss me off again"
Guy 2: " oh you talkin about ole dehoff.. yeah dude that's all he does is piss people off.
Guy 1: " yeah he's a snail clown to the death