To sab someone is to completely shut someone close to you out of your life wildly and unexpectedly. To "sab" someone means to block them on your phone, instagram, snapchat, and twitter. Considered a very wildcard move.
Adj. An abbreviation of the insult "Scrawny Acne Boi" used commonly by people within the 13-17 year range. Can be used both ironically or unironically depending on the intended receiver of the term.