Evolution has created this wonderful thing called stress. We tend to think of stress as something negative that is to be avoided, and that is certainly true: prolonged periods of stress will do all sorts of damage to your body and mind.
However, for short periods of time, stress is a wonderful invention that lets us survive situations we otherwise wouldn't: when we come under stress, when that sabre-tooth tiger pops out from behind the bushes, our autonomous systems produce anti-inflammatory agents, dampen our pain reception, flood our system with performance enhancing drugs, improve our perception, shorten our reflexes, increase our energy levels … and, yes, also repress our sneeze and cough reflexes.
Have you ever had the experience that, after a long period of stress, just when you were finally looking forward to some well-deserved vacation, you get sick at the most inopportune time, right at the beginning of your vacation? Well, actually, you didn't get sick, you were sick all along, but during the stress period, your body suppressed the symptoms, and as soon as the stress goes away, the illness, wich may have been brewing for days or even weeks, breaks out in full.
So, to answer your question:
What if a aerobatic fighter pilot sneezes in middle of a maneuver?
He doesn't. Stress will prevent him from doing so.