Another term for a friendasaurus, the ugly friend of an attractive girl, who is usually there to make the good looking girl even more appealing. The term tyranenormous rex generally suggests that the ugly girl is of beast or dinosaur like size and attractiveness.
When you're fucking that bare muff and you become so pleasured that you lose the capability of your arms and you become a paraplegic. This makes your arms resemble a T-rex's arms.