1. (1) Punishment or reward for one's actions; (2) getting what you have coming to you; (3) getting what you deserve; (4) karma. Commonly mispelled as comeuppins.
    Craig kept talking shit about John that night, so when John kicked Craig's ass the next day, Craig got his comeuppance.
  2. More accurately described as a colloquial phrase, it means "your deserved reward or just due" for an action taken or statement you have made. It always conveys that to be of a negative nature. It should be hyphenated as neither word, of it's own definition, conveys close to the meaning of the combination of the two; therefore the linkage of the hyphen is needed.
    "Joe has always bragged that he was the team's best batter, but in the playoff game he went 0 for 4 and humiliated himself." (Joe; therefore, got his just due or his come-uppance for his continual bragging and then, his abysmal failure.
  3. A "reward" i.e. well deserved and long awaited revenge for past misbehavior. The "reward" should be administered by those previously wronged and in a public or humiliating way.
    That bitch will get her comeuppance in the form of a public birching at the next group pot luck. Everyone there will be quite pleased at the chance to participate. I don't think she will be able to sit down for several days.
  4. A punishment you deserve for doing a bad thing
    You're a cheating git. One day you're going to get your come-uppance.