Dunking things in liquid oxygen then attempting to set them on fire.
Coming back from a night-on-the-town in a foreign country only to realize that I left my ID in the barracks, so logically rather than call my roommate I find a darkly lit corner of the perimeter fence and climb 20ft over it and through the concertina wire on the top.
Catching a drunk military guy attempting to steal an armed military jeep with a K-Bar in his hand, and holding him at gunpoint with one hand on the bottom of the grip so he cannot see that there isn't a magazine in the weapon (no cartridge in the chamber either).
Sitting underneath an F-4 Phantom in full afterburner.
Marshalling an F-5 into its spot on the flightline and letting (trusting) the pilot to stop when the pitot tube lightly touches your sternum.
Partially squeezing through an opening between two 10 ton hangar doors to reach the 'open' button on the inside only to feel (not see) a set of buttons that are unfamiliar to you, so you think 'I'll just quickly tap one to see which way the doors move' and I'll figure it all out, only to tap the 'close' button first and have it squeeze all of the air out of your lungs (cannot yell for help now), so you strain to reach the 'other' button, open the door and fall onto the hangar floor trying to recover.
Going 178mph on a BARF rally.