More than a few times over the years I've been on a flight as a paying passenger (employer bought the ticket), in uniform because the employer required it, and have been dressed down by a captain for failing to check in and get permission to ride. I understand, if the captain has felt that a breach of etiquette occurred, he might educate me on his limitless kingdom and my small place it in, but as a passenger with ticket in hand, that level of arrogance doesn't impress.
When I leave an airplane as a passenger, I nod and say thank you to the flight attendants, and if the flight crew is there, to them, too. Beyond that, I don't feel inclined to fall at their feet and thank them profusely for their generosity in allowing me to buy a ticket and ride. Perhaps that's a misstep, but it will have to do.