An onomatopoetic representation of the sounds produced from various sex acts. This includes, but is not limited to, ejaculation, penetration, masturbation, and oral sex upon a male. It is sometimes used in place of 'spooge'or 'splurt' as a sound-effect, but not always.
When vocalized or pronounced, it is similar to the sound of hacking up phlegm, but with a little bit more of a sibilance at the beginning of the sound-effect, and less of the usual hard 'h' sound.
This soud-effect is sometimes used in reply to seeing or hearing something that would, in the viewer's opinion, lead to or be worthy of any of the aformentioned sex-acts.
Bradford: Hey, look at that hot thang in the miniskirt!
Ollie: Squick! Squick-squick!
Fortinbras: Aw, nerts. The sound's out on the telly.
Magda: No problem! I'll supply the dialogue! Squick-squick-squick...
Fortinbras: Hey, that's sick!
Magda: Come on! You've never thought Mary Tyler Moore needed a little more pizazz?