Not a teacher.
Oh wow. There are so many ways to describe this kind of person. How profane do you want it?
Usually, we would use any number of our colorful swear words, or a new combination of swear words, to make fun of this guy. Or we are very sarcastic about it. Let me think of some clean ways to say this:
You can simply call them a "failure"
They are "too big for their britches" (not really common here, but it can be used)
Sarcastically say "Oh yeah. You're cool." even if you aren't talking to the person. This is the one I use, but you need to hear it vocalized to really get all the sarcasm.
Sarcastically say "He's slick." or "You're slick" if you are talking to them.
We don't really have a specific word for people like this, but they are certainly not scarce around here. Maybe the Brits have a more specific word or phrase for that.