I was on a DL CRJ at Detroit which boarded, closed doors, pulled away from the gate, taxied in the wrong direction for the entire length of the terminal away from the runways, taxied back the entire length in the right direction, stops at the runway then says were now number 1 for takeoff and just departs anyway.
I didn't see any another planes with similar movements.
I can't think of any other reason except "pilot wants to go for a drive?"