A few days ago I was in a Suzuka 750PP race, and after the usual first corner carnage I was moving back up the positions, and keeping pace with a fast guy in a Ford GT LM in front of me. He could clearly drive quickly, and I couldn't gain any time on him (me in my Z06 tuned). But every time he moved to pass someone ahead you saw him take the inside line to a corner and nudge the other guy onto the sand. This happened 3 out of 4 overtakes until he was in the lead and I was second.
If I could have caught him, I would have been sorely tempted to consider giving him a nudge. The stupid thing was that he clearly didn't need that kind of behaviour.
I personally refuse to deliberately nudge people off. However sometimes I am trying to get round slow guys while regaining positions after being hit off myself and it's effectively impossible to get past without colliding with them because they weave all over the place in an effort to keep you behind even though you are clearly considerably faster. After a few corners of weaving you can be fairly sure that they won't let you past on the straight either without attempting to push you into the wall, so in that case I tend to wait for a chance to get past where they are most likely to outbrake themselves. But patience can be difficult