I actually have two biggest pet peeves when it comes to query letters.
The first is people calling me sir. Which isn’t a frequent problem, but it does happen. I’m going to assume that you’re too smart for that, though, and focus on my other pet peeve which even smart people do.
I get so many query letters that start something to the effect of “Billy Bob was a normal teenager until…”
I don’t care that Billy Bob was a normal teenager. Really, I don’t. So maybe Billy Bob was a normal teenager until he gained the power to telepathically communicate with sloths. Why don’t you just say “Billy Bob’s ability to telepathically communicate with sloths just might save the world.” More interesting.
Why is this a big deal? You have a limited amount of time in a query letter to grab my attention. Don’t waste words telling me what’s normal. I am going to assume everything is normal until you tell me otherwise.
In linguistics (which is what my degree is in) we would call this a violation of the Gricean Maxim of Quantity. I say that mostly to show off and also because I like to take every possible opportunity to prove my degree is not useless. Basically what it means, though, is that in normal conversation, we don’t waste time by telling people things they already know.
It would be like walking into first period with your friend and saying, “We’re at school.” And you’re friend would give you a funny look and be like, “Duh. Of course we’re at school. Why are you saying that?”
So don’t tell me your character is normal. Even if they are. Focus on the conflict of the story and what makes them unique.