What is T Rex?
A cheap ass. The person, who at dinner in a restaraunt when its tip time, whos arms seem to be too short to reach into their wallet and tip their fair share. T rexes, frequently seen reusing napkins and relying heavily on the "if its yellow, let it mellow" flushing principal, are the utmost cheapest, tight waded, penny pinching bastards around.
Frank: "Steve, how much did you tip?"
Steve: "I dont believe in tipping... *leaves table*"
Frank: "You god damn t rex... *shells out more cash*"
When you are doing a girl from behind, preferably close to the edge of the bed, and you grab her by the shoulders and lift her up. This results in her swinging her arms aimlessly like a T-Rex while making moaning noises.
"Dude.. what was all that noise.."
"Oo.. I t rexed that bitch"
When your lady is in the "reverse cowgirl" position, you put clench your hand with the middle knuckle raised (similar to the frogging punch). With this protruding knuckle you then place it on her spine and rub back in forth. The feeling is very intense/ticklish. It will cause her to moan in a weird fashion and her arms will become incapacitated past the forearms for a brief moment.
Some women also seem to do weird things with their mouths during the moment.
man 1: "my girlfriend is super mad at me"
man 2: "why is that"
man 1: "I was T Rexin' her for a while and now she has chronic back spasms"