According to the FX show "The League", it is when a completely lopsided trade offer in a fantasy sport is accepted. It typically opens happens to n00bs.
Person 2: Nice, who'd you get?
Person 1: I got Jamarcus Russell and traded Peyton Manning.
Person 2: Dude, you just got trade raped.
Trade Rape 2: Aaron Rodgers, Calvin Johnson, Joseph Addai for Ben Roethlisberger, Cedric Benson, Knowshon Moreno, Mario Manningham
Trade Rape 3: Jermichael Finley for Darren Sproles and Dallas Clark
Any trade completed by a franchise known as Out of Spite.
Me: Dude, Vick and Mathews are the two most injury-prone players. Was this consensual or was this full-blown Trade Rape?
Carl: No, and he said that if I tell anyone, he'll hurt my family.
No! You totally traderaped me last season!
I didn't traderape you! I gave you Vick for Adrian Peterson.
You didn't tell me Michael Vick was in prison.