I've never really had people question me, I find that the check-in staff generally don't bat an eye, and the GAs usually have much more important things to worry about. The only time it was an issue was with a rather self-important GA (actually...might not have been a GA, but some other staffer) who was going around the boarding area issuing gate check tags. They'd announced that all non-F travellers would need to take them. I was F on that leg. He comes up to me, gives me a tag, I politely decline, explaining that I'm in F. He didn't believe me, and I assured him that I was, showing him my ticket.

He got really obnoxious, and asked if I'd booked this or whether the check-in staff had made a mistake. (At the time, I was 20, and admittedly dressed fairly typically for a college student) Took my ticket, went to the counter, gave it to the actual GA (she didn't really seem that interested, probably had actual work to do). GA did something, handed the ticket back to him, and he came back and gave me my ticket without a word.

Very strange behaviour. But I've never had problems from normal GAs, FAs or check-in staff. I'm sure they see far stranger things than me! Occasional harassment from lounge dragons, though.