The appropriate response when someone tells you a far-fetched story that sounds like total bullshit. Said facetiously and with laughable amounts of sarcasm. Similar to "Ok there, bud!" or "Cool story, bro!". The "Chuck" part of the expression is said to have come from Chuck Norris, who was pretty badass. Because of this, the expression is usually uttered by a listener following a totally fake story about feats of skill, strength, smarts, etc.
Guy 1: "K so I drop kicked a guy in the face while he was attempting to mug a chick, and then i saved her baby from falling off of the building. I then went inside of her apartment and railed her soooo hard."
Guy 2: "Ok, Chuck! That's total shit!"
Guy 2: "Ok, Chuck! That's total shit!"
by Disco Stu number 2 December 3, 2010