Sweet Cracker Sandwich is a phrase, first created by MT and then used later by GlatorianJaller, used to annoy people, particularly Mange. It was first used as an expression of surprise by MT when he talked to Mange on the phone for the first time(which got a "wtf" in response from Mange). Later, GJ decided it would be funny to call Mange and annoy him with that, so MT and GJ did that for the next 30 minutes until Mange threatened to never pick his phone up again. So MT and GJ stopped, and neither has called Mange since(except MT one time to discuss the virtues of a Blackjack Taco).
It is the official saying of MT now, and possibly GJ too.