1. To make one feel sick or disgusted.
2. To squick over a bizarre and distasteful situation.
3. My friend Brad in a speedo. *mentally squicking right now*
ie. "Dumbledore, McGonnagall and the Giant Squid are having a threesome and Ron is getting it on videotape."
Disgusting, icky, weird, often referring to something that is squelchy - imagine poking a vat of goo, and the sound you will make is similar to "squick".