I may not have a GT but I do like to show stuff up in my sporting :P
My personal favourite was a friend of mine who had a Lamborghini yellow painted, completely standard MR2 non turbo.
He was all mouth saying it could keep up with my mate Dan's tyre R so on a private bit of racetrack, I raced him in my sporting and stuck to his rear bumper to about 95-100, because he drives like a pussy.
Best bit was I had a mate in the car, and so did he, so I had witnesses.
When we pulled up he was saying 'oh I pissed all over you' etc etc, untill both mates turned round to him and said 'err, no you didn't!'
It was brilliant!