Once I've worked in a start-up located in an engineering university "incubator", so we had a lot of engineer-to-be students applying for part-time jobs.
One of these kids was hired by my boss who labeled him "highly technical, very skilled in IT".

One day, while very busy with my own upcoming release, I had to help him finding a bug in his (horrible) code.

Me: Oh, that's easy, you need to load the image from the parent directory
Guy: ...
Me: You know how to do this, right? You're 1 exam away from being a computer engineer
Guy: ...
Me: Ok, ok, don't worry. Just type "../" right before the path

The guy starts typing, literally, "dotdotslash" into the path.

I immediately stopped him, almost crying. Then, I asked him to go for a walk.
"Don't mind about your bug, I'll take care"