Phil's Rambling Rants
As I understand and have always used the word, "Squick" comes out of the online BDSM world (specifically ASB/alt.sex.bondage, which used to be a really good newsgroup) and is used to describe things you wouldn't do. It is also usable as nearly any part of speech.
"I was squicked."
"That's a trip on the express train to Squicksville."
"Careful, she'll squick."
I've been using this word since probably not all that long after it was coined, and you're right. It describes something that is simple indescribable by any other word.Here is the Wikipedia entry.