This tapping the back, getting caught up and so on is sometimes just close racing. You could be following someone really close and then the person in front makes a slight error/or the track is deteriorating and you hit the back of them. I think in a perfect world we all would miss each other and there would be no incidents. The fact is there are mixed ability heats and its got to be expected, just carry on and do the best you can.
On another note, when watching F1 most weekends during the season, taps, touches and close racing happens all the time. You don't see Webber, Massa, Grojean all pull over and let the person behind pass on race day when they've had there front wing ripped off or been tapped from the side.....
Something that has also been mentioned above, marshalling, is an issue, with certain individuals not marshalling as they would expect to be.
PS. its only RC car racing, if it gets to the point when your hurling abuse, you need to have a word with yourself...