Someone is "doing a Trump" if they throw an extended and disproportionate hissy fit when they lose. Especially applicable if they're an adult and really should know better. Often accompanied by unfounded accusations of underhand activity supposedly carried out by their opponents, and/or false boasts about being the winner.
Usually the effect of "doing a Trump" is to make them look far worse than simply losing could ever do.
Donnie's just lost at poker and he's been doing a Trump for the last half hour. Hahaha, now he's calling everyone else cheaters and saying he's the real winner!
Yeah I'll play Mario Cart with you, as long as you don't do a Trump like last time, 'k?
When you irresponsibly or prematurely walk away from a math test or exam, instead of waiting until the end of the paper, when everyone is allowed to leave the room, because you can’t handle the difficult or brain-unfriendly questions, especially after boasting to the whole world that you have a “geniusIQ.“
During the 60-minute math test the other day, everybody was surprised to see Don do a math trump, who consoled himself that he could always pay a Shapiro to sit for his SAT if he failed again.