In all seriousness, I've been flying since way back when airports did not even have fences. (Actually, they were called airfields back then, but w/e.) And flew a fair amount in the 70's when hijackings seemed all so frequent.

In all that time, the singlemost fear-generating situations have been seeing one or more visibly intoxicated men get on the plane. It's almost never ended politely. Tho thankfully never with physical injury.