The act of defecating, specifically when the load feels like it may explode, and when it is quite probable that you may die when it blows. Originates as a play on the Muslim group, the Shiites, whose religious title looks remarkably like the English word, "Shit." Needless to say, they are probably well aware of this resemblance, and will laugh uproariously with the extensive, nay, global usage of this phrase.
John: Good God! I think this is gonna be a suicide bombing!
John: Pull the fuck over! I gotta go drop a Muslim!
(Sadly, John did not make it)