Somebody, typically male, who makes more money than they should and is a douchebag to others who make less than him.
The word comes from the fact that cupcummers would make a lot of easy money from sperm banks by cumming in cups. A cupcummer is then someone who, undeservedly, makes a lot of money just doing simple things (i.e. cumming in a cup). Cupcummers are often, but not always, materialistic assholes who show off their expensive things (that they didn't earn) to make others feel bad.
I can't stand Bob from accounting, he's such a cupcummer!
Who does that cupcummer think he is in his Porche?