Let's say: You're very good at computer stuff, such as programming, fixing hardware, etc. When it comes to things like that, you're one of the best, if not the best! And one day, a friend comes over to your house, using your computer and talking non-stop about why you should use these software instead and not those ones installed in your computer... things like that, even though you have much better knowledge in this field than him. I mean your friend is trying hard to show-off his skills without having known that the person he's talking to (it's you) is miles better than him.
So which phrase should describe this situation the best?
Edit: To be a little more specific, I am looking for a phrase (if it really exists of course) to describe the friend's action, so it can be used for the expert in that situation to say or another friend/third-party which happens to have listened/seen the conversation/action. For instance:
Your friend named A (less knowledge than you): "Man, you should've installed Windows 10 like I said than this useless Linux distro, and believe me when I say that, it can't even install some common software like foobar."
Your friend named B: "Lol, A, please just stop, don't try to make fun of yourself here, he knows much better than you when it comes to things like that."
So what I want here is a phrase than can be replaced with this line: "don't try to make fun of yourself here, he knows much better than you when it comes to things like that."