Abbreviation for Cringe, Wither, Die (or cringe, wince, die).
Used when something particularly disturbing (ohmygodIcan'tbelieveIjustsaidthat) has been said.
Basically, it's a more modernized version of TMI
A: Holy shit, I saw this kid with acne ALL OVER his face today. There was acne on his forehead, arms, neck, cervical-
S: Oh, Lawrence? yeah, remember the guy I told you I lost my virginity to? That was him.
A: CWD CWD