I host a room every night and have a bunch of regulars. However I still keep it open to pubbers. I have to kick one or two people a night, but never for winning a race. Sometimes the racer is the winner but the actual reason for the boot is due to something along the lines of...
1) Driver has bad lag and bounces around on the track making it impossible to pass
You may not be aware of your own lag so if someone says "Driver X is lagging" you gotta go. If you aren't sure, check your rearview. Do cars crash when you pass them? If yes, you've got lag.
2) Driver doesn't understand the restrictions that are outlined in the lobby title.
I give drivers a warning and I check the field before starting the race. If I see a race car in a street car lobby, I'll boot you before the race starts.
3) A complaint is made about a driver and is verified by another driver. Aka rough racing.
This isn't baseball, you don't get 3 strikes. Race with restraint or find another lobby.
4) Driver punts me on the first lap.
First lap, tires are cold and everyone should be prepared to brake early as cars stack up entering the first slow turn. If you think you're going to pass 4 cars on turn 1, you should be racing A-spec, not online. Everyone in front of you put down faster qualifying laps. Give them the benefit of the doubt that they know how fast to take the first turn.
So if you are constantly booted from lobbies, step back and thing about these items. Is your internet connection decent for lag-free racing? Are you coming in contact with other cars when you try to pass? Are you racing a car that is equal to the other drivers in the lobby?