As one who wore a Tash throughout 30 years in Her Majesty's RAF I had at various times some interesting discussions about the styles of moustache that could be worn as the regs only quote a minimum, i.e., the entire upper lip must be unshaven, presumably to head off any A...F H....R styles, therefore leading to some discussion at times on the maximum lenghth involved. I do have some photos of my upper lip in the 60s in Cyprus in the popular Viva Zapata style, with a good tan very Mexican, this at the time was kept by explaining that it was an inverted handlebar moustache, and I got away with it for a while, I was on the M.U. which was a world of its on!
Whilst on the Herc as a G.E. we had a captain who had a full set for medical reasons, seems he had no problem with it and oxygen masks, mind you the only time Herc crew wore oxy masks was for a quick puff in the morning to get the brain back on speed!