Leave the room find a new one..profit. This is and will always be the case for online gaming (which may be the reason I find myself enjoying offline single player games more and more).
The good thing about GT5 is you can host your own room, and kick whoever you don't want in there anymore. If you come into a game that Im hosting, and you sound like your balls haven't dropped yet, you'll probably get the boot. Or if you just come in and talk like you're half retarded before the race even starts, you will also be kicked promptly.
That appens in all games when i played race driver: Grid and NFS shift online it was the same thing there where always someone there just to block smash your car into walls or out of the track.
I can't play online now so i don't know so here's the question ,GT5 doesn't have the option to kick players out of that lobby or a vote sistem to kick someone?