2. A pissing sound.
3. A sound used to call attention to someone in quiet cirumstances for a pseudo-slick impression.
4. A trick. The psst sound is draw, they come to wisper something in your ear while another kid sets up on all 4s behind your legs, then you're on your ass. Usually followed by a, "hahahaha, idiot." and sometimes a gunshot.
Dude! Quite peeing on my desk!