I’m going to be honest with you, I do not know why/if this is funny. Frankly, I’m not sure it makes sense at all.
I was sitting around thinking about washers and dryers (as one does) and trying to come up with a third option and this presented itself. It’s pretty weird.
I think it would work better if “supervisor” ended in “-er” but maybe not.
That being said, this cartoon does make me laugh. I cannot for the life of me explain it, but there you go.