If I am flying with someone, I have no qualms about taking control and telling them what I think. It's my life in that cockpit as well!
That could just as easily lead to an accident as well! Whilst you may judge the other pilot, who's judging you? You could have the situation wrong and contribute to, rather than prevent an escalation of errors. If you are a passenger in a friends aeroplane that you have not flown, would you take over in the last seconds of a bulked landing say? The owner may just be getting things under control, when you come in "cold" and spoil the day. This could just as easily happen with an experienced instructor in such circumstances, so I'm not suggesting your pilotage is in any way below that level. OK in some situations you could well be correct, but as a generalisation, surely it's best to let the flight finish and then comment, bollock or even smack said pilot on the nose!
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