He has my sympathy
I was caught in a similar situation at Heathrow a couple of years ago. I'd had too many cups of coffee while waiting to board and then, after boarding, the aeroplane got stuck in a very long queue waiting to take off (nearly 45 minutes).
Fortunately, my seat was next to the toilets. I unfastened my seatbelt, dashed to the cubicle and locked the door before the stewardess could react. Within a minute I was back in my seat, buckled in and feeling relieved but rather embarrassed (everyone was watching me). The aeroplane had moved forward about 10 feet in the meantime.
The stewardess gave me a dirty look but decided not to make a fuss. That was Qantas. Perhaps they expect that sort of thing from Australians.