Boss thinks I'm dumb, now what?

Others have already given good advice of the form "leave the company", etc. I don't disagree.

But consider, maybe he explains things like he does regardless of who he is talking to? Sometimes the best explanation for a junior developer is also the best explanation for a senior developer. Do you have any other reasons to believe he disrespects you?

You probably want to tell your boss "stop disrespecting me and giving me junior level explanations, stop being patronizing". Of course, you can't just say this... or can you? You can probably find a way to say this if you "grease it" with enough respect. Find a way to be honest and respectful. Maybe something like "I appreciate your explanation, but I'm having a hard time following. I think it would help if we could talk about things in higher-level terms I'm already familiar with, I already know what an API is so we can just talk about API's without going into more detail, the extra detail is distracting me from the thing I want an answer about, etc."

Just trying to give some advice that might help if you want to stay. But again, leaving might be the right choice too. Your call. It would help if you would be a little more concrete about what and how he speaks.

It helps to give him this feedback and not us. I work with a lot of people with varying levels of expertise in various technologies at various levels above and below me. I generally make no assumptions & rely on them to tell me when I'm telling them something they already know. After all, for all you know, the last person he explained something to needed it broken down so simply.

It sounds like neither of you are being very effective communicators.

Your boss should be a better gauge of your skill level and adjust his language accordingly.

On the other hand it's on you to tell him that the level he is communicating at isn't right for you and he can skip the explanatory stuff if he's doing it for you.

It would be helpful if you were more concrete, otherwise there's no way to give meaningful answer.

That may just be his process. He explains things to help himself understand it better.

I would be THRILLED to have someone who wanted to explain things like I was 5, lots of people don't

Have dealt with this a couple of times. I see you're feeling some kind of reaction. I recommend talking it out with someone (professional therapist or otherwise). Often times a frustrating relationship has a clear path to amelioration, but it takes "seeing with fresh eyes".

Find a new job, or if you like the job you have just ignore it. Or if you want to get fired start explaining concepts to your boss.

There is a chance that he is well-intended and he believes in starting from first principles - think ELI5. It would be interesting to hear more concrete examples.

Are these explanations actually relevant? Perhaps your boss offers them because you have different approaches about some basic topics?

Can you give an example?

Have you told him you feel this way?

One of my biggest annoyances with devs is that they rarely give "upward feedback". They expect their manager to just magically know how to manage them, and they complain if their boss gets it wrong. You can just tell people though - say "I'd like to give you some feedback that will help us work better together..." and explain what it is that you find annoying. If your boss isn't a dick they'll take this onboard and change.

Everyone should learn to give better feedback. It's one of the things that separates a mediocre team from an awesome one - people actually trying to work together better.

Have you asked your boss why they're treating you this way? If not, that should be your first course of action.

I don't see enough detail here to really advise.

Please consider having fun with it or getting promoted over him.

You've probably read that the biggest reason people leave their job is because of their boss. Not the company. Not the work. Their boss.

Now you're learning why.

Leave the company.

If your boss wants to be king of a shithole with his behaviour, he will be the only person in the company or the company will fire him.

Life is too short to deal with people who are disrespectful to your expertise and think they either know better than you, condescending, manipulative or are passive aggressive.

If you leave the company and tell others how bad the boss is, they might follow you in leaving as well.

To what degree do you have control over this person's actions?