F/O told me a tale; while taxiing for t/off, Capt (reputation for being a stickler- and I'm talking recent, not Imperial Airways days), suddenly notices that said F/O had removed his tie; put the park brake on right there and then and told him to put tie back on, which he did. Another day, another F/O, same Capt, similar scenario, but this guy decided to tell the Capt to "Foxtrot Oscar", or words to that effect (nothing in company regs requiring the wearing of ties on the flight deck).
I guess it takes all sorts to make the world go round.