Literally everything. This kid had no ability to be in a work environment.
I had this coworker who will be called Gabe.
He was hired during my third year working as a "Cash Lead" in an amusement park. It was technically not an entry level position, which is why were were called "leads", but in reality it was one of two positions that were bottom of the totem pole in the department. We were the people who took cashiers off register and counted their tills. It was a very fun job in some aspects, but also really stressful and under-appreciated. As a result of that and the 18+ age requirement, it did not have a very high retention rate. It was especially desperate times that year, and we were even hiring people 2 weeks before the park closed.
Gabe came in on a day when I was working "inside" in another position that focuses on entering the information from each till. I was one of the few people that had been cross-trained and, like I said, we were short on people. As a result, I didn't really get to meet him with everyone else. The following day I was off, but I got a weird text message from my friend Jed. Something along the lines of: "Oh my god, this kid Gabe. Just wait."
The next day I worked I came in for the second half of the day, after I got a call from our boss asking for people’s help because of no-shows. I came into the garage of the bank and saw him tossing somebody's stuff out of a locker. We don't have official lockers, but generally we'll claim a locker by putting an extra nametag on the one we use the most frequently. Since we can't carry personal bags (or money of any kind) in and out of cash control, they're central to our existences. As you probably expect, that means there are a lot of unwritten rules about locker use. Not only did Gabe not pick up on those mores, he completely disregarded any sense of courtesy. After two days he had decided that particular locker was his, and whoever had put their stuff in there had taken his spot. He tossed all their stuff on the floor, put his own wallet in, and placed his jacket on the door of the locker. It was a big no-no.
Now, Gabe was apparently having a really hard time with the job. More than even me, and I had sucked at the job for an obscene amount of time. Generally, on the second day of training we are weaned away from the person who is training us, and the following day you are thrown to the wolves. It hurts, but the basics of the jobs aren't the part that most people struggle with, so it's not usually disastrous. Jed had been training Gabe both days, and told me later that the kid had absolutely no ability to retain any information. He had tried desperately to get Gabe to understand the system, but could not physically leave the guy alone, because everything would fall apart almost immediately. Jed was the guy that trained me, and I can say with the utmost certainty that he is one of the most patient and competent trainers... but there was nothing that could have helped Gabe. On his third day, when he should have been alone, one of our area managers had to accompany him to each of his registers, and walk him through the buttons to push to get the till, how to fill out the CTS, and how to do the math to figure out if the register was ok. That same guy, Roger, was essentially working as a lead of one area, a supervisor of three, and holding Gabe's hand through EVERY count-out. Roger approached me and offered to take my area in exchange for me acting as Gabe’s trainer. I was excited, because as one of the people who had not picked the job up quickly, I was not generally someone given responsibilities like that. I swore to myself that I would be the best trainer that had ever existed. I wish someone had warned me. I wish I had thought about what kind of person would need this level of hand-holding.
Three days into his job, I asked Gabe to do a count out so I could see what I was working with. I can’t even describe to you how little he knew. Actually, I can: Less than nothing. Not only did he take 30 minutes to count a till (something that isn’t unheard of with new hires) but he seemed to have received absolutely no training. So I just started walking him through everything again. Gabe apparently had no inclination to respond to instructions, questions, or small talk, so I just rolled with it and kept the narrative going. We fell a few minutes behind, but his count-outs were scheduled lightly by his supervisor, so I wasn’t too worried about it. But it kept happening. He was actively sabotaging the count outs, writing information down that went against what I was telling him to write, because he thought he knew what he was doing, and that I was mistaken. I kept trying to explain how to add credit cards, and he would tell me I was wrong. I would tell him how to calculate the end reed of cashiers who were on register previously, and he would say that it didn’t matter, because the computer already knew. The computer did not already know, and doing that calculation wrong added between 10-30 minutes of work to the tellers who keyed the till bag into the system. Something no one wanted to deal with when a bag should only take 5-10 minutes, and you do not want to piss tellers off, because they will remember you.