There are people out there who are experts in one thing or another and that gives them an advantage when writing certain things. The thing about being an expert though, it puts your readers at a disadvantage if they can't understand what you're talking about. 

If your character speaks fluent Latin and they go around spouting off phrases in Latin without any explanation of what they're saying your readers will quit on you very quickly. They won't have a clue what's happening and they won't continue to read.

If your character is an expert mechanic and goes off on a rant about how to fix a vehicle properly, and you never explain what they're talking about, then your readers will skip it because they won't have a clue what your character is talking about. 

You don't want your readers skipping large chunks of the book or to stop reading altogether.

Readers don't want to feel stupid. If they feel the author is talking down to them simply to show how smart they are, then why read the book? If you're going to shove paragraph after paragraph of technical data at readers, then you need to give them explanations of what that data means. If you make your readers feel inferior, then they aren't going to want to read your work.

To give you an example of well-written technical books, read just about anything by Michael Crichton. The man loved technical data, especially science stuff. His books are well written, and they don't talk down to you. His books are exceptional. 

There is certainly nothing wrong with writing a character who is a smarty pants. You simply need to make them relatable to the people who aren't experts in the field. Don't make them a know-it-all who doesn't explain things. You can have other characters give them a nudge that reminds them to explain things. Just think of the show Bones, Temperance Brennen is a major know-it-all, and she isn't afraid to let everyone know she's smarter than they are. Often, Booth is the one giving her a nudge to explain things because he rarely ever understands what she's saying. Throughout the show, Tempie maintains her know-it-all attitude, but she changes and grows, and she begins to acknowledge that knowing everything doesn't always mean you're the smartest person in the room. If your characters can't grow and learn, then people will get bored with them. 

A while back, my friend read a book on here, then passed it along to me and was like, "You have to read this. I have no clue what's going on." The author had the characters constantly spouting Italian, with zero explanation about what they were saying. And it wasn't simple phrases, like ciao that most people would understand. It was long strings of Italian that you couldn't decipher. I took two years of Italian, granted it was way back in high school, but I had zero clue what was happening. She and I spent some time trying to look up the phrases, but doing that pulls you out of the book, and it's certainly not how I want to read a book. Your readers shouldn't have to spend their time researching what your characters are talking about. 

Make certain your characters are believable and understandable. You want your readers to be able to relate to them, not shun them. If they can't find anything relatable, then they'll put the book down and move on. And if they truly hated the characters, they won't be shy about telling others to avoid your work. One thing I've learned after many years in retail: people will tell everyone they know if they have a bad experience. If they've had a good one, they will tell only a few people. Sadly, that's the truth. We rarely shout about a wonderful experience at a business, but you hear people spouting off a lot about bad ones.