somebody who has no consideration for others and will go to desperate measures to get what they want. usually a person that is significantly older than his or her 'friends' or persons of using. this person can also be best friends with somebody and absolutely hate them for absolutely no reason. many people will hate and rally against this marybitch, but the marybitch will fight back using a large amount of profanities and threats.
person 1: dude, I saw a marybitch yesterday!! he was so fucking rude to everybody!!
person 2: I know, all marybitches are known for being total assholes!!