I had that 'mediocre driver issue' this last weekend, and fortunately he broke 1st lap of the main and I was happy because previous heats he would just take the inside way to fast as I was at apex and just t-bone me every time.
If I am slower than the guy coming up to pass me, I will move over, and if I am racing hard against someone, I make it my goal to not even touch them too, and if they have inside, I give it and I just work the outside if possible. I try real hard to be respectful to the other drivers.
However, if it is the mediocre driver, and they are a lap or two down and just driving reckless, I'll follow real close and do a little tap to their rear bumper coming out of a turn when they are on throttle and that is usually enough to make them veer and sway out of the way pretty good. But yea, coming out of a turn is my favorite place to 'tap'.