Well, when I get a blue flag, I know I will be a pain in the ass for the driver behind me. I know the feeling of getting in front, lead and run a bit away from the others, and then to be held up by a backmarker.
When I get a blue flag, for whatever reason, I mostly just lift my throttle a bit on longer straights to let him/her/them pass, because I know that I would have just a little to win, and not much to loose.
Worst situation for a leader when lapping, is when you must lap 2 drivers that are of the same speed. You want to get past, but mostly they are more in battle, because they both want to win from the situation. This sometimes results in wreckless driving, that will only be bad for that driver behind them that is faster.
I had this situation a few times, and one time it lasted for over 3 lps, with the driver behind me gaining on me very fast. After a few times of showing myself in the mirrors, and saying near them so they can see a blue flag, I noticed that they didn't really were going to let me through. This made me deside that I just had to try to overtake them like I do when gaining places. That is not the situation you want to be in. It ended up with one of them pushing me on the grass before a hairpin, I was braking full, but got one of the out of the race because I had no controle, and slided with a good amount of speed in the side of that guy.
That is why I think that, when you are going to be lapped, and you are in battle, you should both give way, and give eachother enough to keep the situation somewhat simular. This is something I consider real gentlemen-driving. But with the competition-instinct of a racedriver, this is something you won't see much. Someone just always want to gain profit from the situation.