Not necessarily a word on its own right, tssss is a handy and fun expression to use in D.F.
It can be used to convey disbelief or surprise, but more generally it is the expression of the sudden realization of something's severe implications or an indication of one's disapproval for someone's conduct.
No manches que te chingaron la feria? ¡Tssss!. Get out, did you really get mugged? Shhhiiit!
To properly deploy it, squinch an eye while mimicking air escaping from a valve. Spreading your palms to the sides corresponds to disapproval, tilting your head back corresponds to sympathy for a tragic occurrence.