Quote from Hatemaker :

I guess I'm a bit barbaric then, because if I'm stuck behind lap traffic that wants to fight me off (I'm talkin' for about a lap or so), I tend to give them a very light tap to show them that I'm behind, and to make them want to obey the big blue letters that say "BLUE FLAG" on their screen.

Totally unacceptable in my view. I'm sure they know you are there without you having to tap them. I can understand your frustration if they do not heed blue flags but two wrongs do not make a right.

I would probably just report them to the server admins for ignoring the blue flag and have a quiet, polite word with them after the race asking them why they ignored the blue flag.

Tapping a blue flagged car can very quickly get you banned from the STCC servers if lag is involved.
Rather tap the horn. That'll help a lot better and there is no chance of accidentally wrecking another racer.

Vain

imo, the closer the race (between the drivers) the bigger the chance of the odd bit of contact. thats why T1 is always so interesting on lap1 (too many cars in such a small space). hate it or not,it's true. rubbing is racing (when said in the right context) when two cars colide, 9/10 times there was no intention to make ant contact at all. these things happen all the time (usually when trying to outbrake someone).