1.One who, or that which, kicks.
2.A fact, condition, or circumstance, sometimes concealed or not obvious, which reduces or eliminates the benefit of an apparently advantageous situation; a joker (5); as, under the Soviet system, bread was good and cheap, but the kicker was that you waited in line for hours to get any, if it was available. (informal)
3.Hence: An unforeseen added expense or additional cost; as, the printer was cheap, but the special paper it needed was an expensive kicker.