Pssht is a greeting.
All you have to do is
stick out your thumb, index, and pinky fingers and say, "Pssht!" whenever you
see your friends.
You can do a behind-the-back pssht or an under-the-
leg pssht, etc.
You can say it really
long, like "Pssssssssshhhhhhht," usually by adding more s's and h's.
The pssht is kind of like Spiderman -- oh wait, except NOT! Notice how Spiderman doesn't use his thumbs, his webs come out of his wrist not his fingers, AND he doesn't say "Pssht."