What are your biggest "Lieutenant mistakes" that you made as a Lieutenant?

Any time a senior NCO says don't worry Lt I got this or I got you covered. You better double check that shit yourself. I've seen many Lt's go down if flames for blindly trusting someone who said I got this don't worry about it.

At the Fort Bliss O-Club they used to have a slot reserved for 'Any 2LT' right next to the General's Reserved slots and before the COL's.

I once stood at parade rest for a CSM...

As a young 2ndLt fresh out of The Basic School, I PCS'd out to 29 Palms for Comm School and was having a blast. When I got out there, it was about that time that we were changing seasons and going from sleeves rolled to sleeves down...but I was in 29 Palms. I always heard things were different out there like they don't switch from deserts to woodlands and what not. I knew we were staying in deserts, but does this mean my sleeves stay rolled also? Confused and not wanting to look like that stupid lieutenant, I decided I'll just run into the PX with NO blouse on. Aha! I can't look like the oblivious lieutenant then. Needless to say, there was a salty grunt MSgt in there that destroyed me for being in the PX in PT attire...

At the Fort Bliss O-Club they used to have a parking spot right next to the GC's for 'Any 2LT'.

I don't know if it was a mistake or not, but we had a 2LT as a detachment commander in Vietnam. Because of the nature of our work, he prescribed our duty uniform as fatigue trousers, white T-shirts, and low quarter shoes.

We were attached to another unit for quarters, rations, and logistical support, and that unit commander (a captain) did not like us coming to eat in his chow hall, wearing fatigue trousers, white T-shirts, and low quarter shoes. He put out a directive that, if you came to eat in his mess hall, you WOULD be in a complete uniform, to include bloused boots, or appropriate civilian attire."

Our lieutenant went to the manual of operations, and found an obscure paragraph, way in the back, that said something to the effect of "At the discretion of the detachment commander, civilian clothing may be authorized as appropriate." He authorized the whole detachment civilian clothing.

The captain was livid, and called our boss in Saigon, who was very jealous and protective of his people. There were rumors that our commander (a Lt. Col.), told the captain to "go fly a kite," but used language much coarser. Something about "urinating up a rope."

I was on watch one morning during my ship's 2010-2011 deployment to the western Pacific and my department head, a LT (O-3) who was in in charge of Operations Department, walks into CIC to see how things are going and talk to the TAO (another LT). He looks at her and says "Why do you always look like you're trying to **** me". There was stunned silence everywhere. I know what he meant, but that's not what it sounded like. The TAO was a female LT.

I took command of my platoon just a dusk on Christmas day. Twenty minutes later, we took two incoming Chi-coms, resulting in casualties. My Platoon Sergeant was off in a second to check on our wounded. The Skipper called me and asked if I could adjust 60mm fire on the suspected source ville.
"Roger." The rounds hit. I couldn't see a thing.
"Dammit, adjust."
"Roger, uhhh, right."
"How far right?"
"Uhhh, right, one village." That's when the Gunny dropped by and got me through the rest of the night.

Not my mistake, but a big one for a 2lt TAC officer in the OCS company I was in. At Ft. Benning Infantry OCS in 1969 my company had just "turned Blue" the day before. While in class that day one of our Senior candidates fell asleep in class. He fell out of his chair and the Captain instructor was not at all pleased. At the end of the day we returned to the company area and were instructed to go to our rooms, take off our senior blue backings and scarves. Then return to the company assemble area. The 2LT had decided we needed to be punished so we were run to the large PT field in front of Infantyr hall. There we began circling the track at a double time.

Shortly a staff car with a flag on the front bumper came bouncing across the field. The 2LT. was summoned to the staff car by the driver. The driver came to our formation and told the Student CO to return us to our company area at a march speed.

Turned out that the LT. had forgotten to have us remove our very shiny Senior Candidate helmet liners with the blue decals. The 2LT was never seen again.
53rd Co. 5th Student Battalion OC. April 69

fell for my NCOs' practice joke... and they put the joke on my going farewell plaque. ;)