When is it acceptable to high-beam slower traffic on the motorway/highway?

Just curious, as I took my darling(m3) for a spin today, and cruised a bit on the motorway just to have some decent high speed fun. I high-beamed 2 guys because the inner-lane was clear and they were going 10 under the limit. Although, is it acceptable? Or just a douche move only BMW owners do?

Personally I don't find it annoying, I would rather have the car behind me high-beam me than to go FULL AUDI