Initialism for Self Injury Behavior. Used in U.S. medical charts to indicate an action taken to harm oneself without intending to die, typically superficial cutting with sharp objects. Compare with cutter.
"The guy in room 15 presented with SIB after his girlfriend dumped him."
Definitions include: so ugly that after a guy has chewed off his arm to get away without waking her, he would later chew off the other arm so not to be recognizable as being a "one armed man" in the event she comes searching for him.