There's a simple and easy answer for the original question-
Treat other racers the way you would like to be treated. If you were leading the race with second place hot on your heels and a lapped (x3) car was in front, would you want him to try and hold you off letting second place catch and possibly pass you? I wouldn't, and I always try to remember we are primarily racing for fun. I love to win just like the next guy, but I don't want to make enemies at the races nor do I want others to think I'm more of a jerk than they already think...
I would rather lose a tenth by taking a wide line than lose half a lap because the leader had to Earnhardt me out of the way.