Generally I will say if I am experienced in a run or not. I honestly don't tell people the mechanics unless they ask. Sometimes people like to experience their first run without spoilers. Sometimes wiping can be the best teacher. When they say "what happened?" I tell them.

However I am never nasty or rude when people are learning. As long as there is improvement even in failure I am pretty happy. If I wanted speed runs I would be finding a static group not DF it.