A guy overtoook me and my better half on the Silverknowes path last night. He was steaming along (not in an irresponsible way, I should add) with his knees out and putting so much effort into his pedal strokes that it looked like he was trying to squeeze his saddle up his fundament.
If I knew the guy I'd certainly have offered him some bike fit observations, but as a stranger, even had I been riding the same speed as him, I wouldn't have raised it unless I was well into a conversation about cycling.
You just don't know how people are going to take that sort of advice and my unconscious bias assumes that blokes of a certain age are more likely than not to react badly to anything that might be perceived (even incorrectly) as a criticism.