Your best "oh crap" moment?

When I was in the guard last summer, we had a MWR/Mando fun day at a bowling alley with a very open bar and staff I can only assume thought we were all 21.
After several beers, cheap shots, and terrible bowling, my buddy and I went out to smoke. My buddy is a lightweight, the kind of guy who smells the cap and gets buzzed. As we light our smokes and start to bs, out walks our BCSM (we were HHB). We immediately go to parade rest. Which is the only part of the etiquette we got right. Over the next 3 minutes my buddy calls him sir, dude, and sergeant, holding a smoke in one hand and a Pabst in the other. I nudged and at one point smacked my buddy, but he was so far up his own ass, he didn't get it. I got all the dirty looks and he ended up getting an award from that SMITH later that day, still drunk.

I was working at the Coast Guard's Ninth District HQ (basically Division/Base/Fort HQ) with a small exchange on our floor, so Coast Guard Auxiliary members would CONSTANTLY be visiting (old military wannabes with WAY too much money and a mighty sense of entitlement). We'd get a half-dozen stopping in every day because they didn't know how to read signs directing them to the Exchange.

Cue the day when this sawed off guy in civvies comes in and starts asking questions. I was an E-5 and my buddy was an E-6, and this guy was polite and seemed happy enough, so we stopped work and shot the breeze with him for about 20 minutes. He turned out to be REALLY nice, and as he looked at his watch and said that he had to go. We volunteered, "Oh, the Exchange is down at the opposite corner of this floor, you can't miss it."

He looked at us a bit funny, and said, "Oh, I have a meeting with the boss. I'm Jim Hull, the new Admiral."

He departed and my buddy and I spent ten minutes trying to figure out if we had stepped on our collective dicks during the conversation. Turns out we didn't, and Admiral Hull was a hell of a boss.

We were in Gagetown CFB, New Brunswick doing demolition training. There was an assortment of items left for disposal - it was in the late 1980's the wild west compared to today - and it needed to vanish so we could pack up and convoy home. In the combat engineer world, P stands for equivalent Pounds of TNT - it also means "plenty". We had plenty.

We calculated we needed to be back at least 1500 feet...perhaps more would have been better. There was a small command detonation bunker with 20 earth walls near the demo point. Two personnel were safely in the bunker. The rest of us went to the "safe point" at the calculated distance. Command detonation occurred: the earth went up taking the shape of a tactical nuclear device - debris went higher than we ever could have imagined....it was coming down in a trajectory towards us...yes, we dove under our 5 T dump trucks and some large hunks of earth fell on our vector about 50 feet beyond the truck. "Oh crap" hardly covered that moment.

There are several other similar stories working with those nearing retirement Vietnam Vets as a young officer...

Not really an "oh crap" moment, but as I got older my white blonde facial hair got a lot darker. So dark to the point where I had (still have but my post-retirement beard covers them up) dark hair follicles on my face.

I was constantly being harassed about not shaving and accused of lying about having dark follicles. It got to the point where I would often have to ask my superiors if they wanted to rub their hand on my face to see if I was lying. A few actually took me up on it and finally believed me, and a few wanted me to "go shave again."

By the time I had about 15 years in the Navy I was one of those guys who had to shave twice a day. If I didn't, I'd have 5 o'clock shadow by the end of the work day.

I was doing a routine engine check on my assigned pusher boat (pretty much a Boston Whaler boat) when I was assigned to Port Services division at Naval Submarine Base Point Loma. I was in the engine compartment checking something on the starboard engine, so my back was to the port engine. These engine compartments were pretty small, so if you moved your arms back at all you could easily brush against the opposite engine. I did just that and felt my left elbow brush against something plastic and move it. I immediately knew what it was, the plastic safety covering for the emergency Halon activation button.

I audibly gasped (too nervous to even say "oh shit") and turned around for a better look. Luckily I had just lifted up the cover and not pushed the activation button. So I closed the cover and completed my engine checks.

When I finished I reported back to my boat captain (an E-5/PO2) and he asked his normal question "Any issues?" I said no but I told him about the little incident. He got a good laugh about it and said he would probably have gotten a bit nervous too, but probably wouldn't have freaked out as much as I did, because I was more experienced than me (I was an E-2/Seaman Apprentice at the time).

My deployment orders.

But it was a different sort of 'oh crap', because I felt I was earning the right to be a soldier more than just going through the motions and not feeling like I was living up to the part.

Doing dumb Private things like saluting privates or leaning forward when I should be doing pushups... or having your thumb caught while rappelling down the wall in Basic... or even falling into the net repeatedly on that single rope bridge and laughing about it...