I usually am pretty laid back about what people do, unless it endangers others.
I will report a burglary in progress, I would report dangerous driving and I would stop a mate from driving home over the limit.
I think I would have to apply the same principles to someone who was clearly doing something dangerous when flying, although I do accept that the current 'system' whereby the investigator is also the prosecutor is not ideal.
If someone did something which did seem 'less clever' and I was in the opportunity to have a chat about it then I would do so although it has to be said that there are a fair few people in aviation who's egos are a bit too big to accept any comments or criticism.
Contrary to what others have written on this thread before I find that those with more experience are usually the more perceptive variety of aviators.
As with most things in life, the longer you're around the more you can accept and admit that you don't know it all!
FD