Since the OP asked if anybody could top that maintenance screw-up, I'll toss one in here that haunts me to this day, nearly 35 years after the fact.
Working as a line-boy on a fine summer CAVU day, I was busy at the gas pumps, squeezing in other activities at the hangar between runs down to top up customer's airplanes. One of those other activities was a request from our chief charter pilot to check the oil in the King Air's PT6's so it would be read for a charter the next morning.
Dutifully I checked the oil and discovered one engine down a quart, so that quart was added. Before the task was completed I was summoned to the pumps so I hastily buttoned up the cowls of the King Air and headed off to the pumps.
Later in the day I had a nagging feeling about whether I had finished the job on the King Air and, being a conscientious fella, I popped open an engine cowl to confirm I had indeed completed the maintenance task properly.
Fast forward to the next day when I show up at the hangar and the King Air is, as expected, away on charter. I barely had my coveralls on before I was summoned to the office of the maintenance director. He was beet red, absolutely livid. He asked for a description of what I had done to the King Air the day before, then, barely containing his anger, told me to get out of his office. Oh Lordy, what had I done?!?!
The news slowly filtered across the hangar floor. The King Air had gone into a very busy airport with one engine feathered. As it turns out, that same engine cowl had a fine pink tinge to its otherwise white color. Yup, that engine had leaked a lot of oil, with the leakage having been detected by a paying passenger. It started when the power was pulled back at the top of descent - the passenger spoke up before there was any fluctuation in oil pressure so the engine was secured without damage..
On the ground the flight crew discovered the engine oil dipstick was laying atop the engine. That was the engine I'd put a quart of oil in the day prior.
You guessed it - I had been interrupted and had not completed the task of adding oil and re-inserting the dipstick. I had gone back to double-check but had checked the wrong engine!!!
No real harm came of this event; a couple of quarts of oil were added to the engine and it was flown back home without further ado. The post-action debrief was pretty explosive. I had a major strip torn off me, which was deserved, but I continued to work and was thankful for the job. The chief charter pilot and his F/O (a close friend) were stood down for 30 days without pay for having failed in their duty to conduct a thorough pre-flight inspection. AND they had to wash the airplane (normally a duty reserved for the lowest man on the totem pole... me!).
To this day I don't recall the details of the dressing-down I received as a result of my maintenance oversight. However I DO recall in vivid detail the shame and horror that I felt the moment I learned that I had not properly replaced the engine oil dipstick. It was the most awful stinging painful sensation that almost made me double over - like a hard kick in the guts.
It's the memory of that feeling that makes me check and double-check to ensure dipsticks, fuel caps etc are secure before a flight. That one small screw-up has kept me vigilant for years.