It basically means to leave someone alone when they do something wrong. Also used as "spare me some". Example: at work, you may have done something wrong. Your boss is screaming at you, and you use this phrase.
Boss: "You idiot! You made this company lose one billion dollars!" You: "Calm down boss. I'll pay it back. Spare me some shit."
by Singled_Out_alone May 11, 2014