People who say "nucular" strike me as being completely brain damaged.

Also: ATM machine. So...the machine machine? Not just the machine?

I assume I'm unusual because whenever I say an acronym I think the entire phrase. So repetition like this grates on my nerves.

People do this with other acronyms...can't think of other examples now.

The most grating to me right now has to be the comma splice (run-on sentence). For example: "Every one of our talented art students will have artwork represented in the show, it is always an impressive event."

I see it everywhere lately! Even in official business/marketing emails. Someone got a college degree and got hired to write that email ffs. Use a damn period or semicolon.

"In terms of" when it relates to nothing in the discussion. It's just a fluffy pile of nothing to either make you sound smarter, make your idea sound smarter, or fill in space like "um".

"In terms of the design, we're choosing blue."

"Anyways". Don't fucking add the s to the end, it adds literally nothing but costs you more effort. Say or type "anyway".

"Also too" drives me up a wall.

OP, thanks for asking. I feel seen.

1. Using the past tense instead of the subjunctive mood. "What if she was gone?" Nope. It should be "what if she were gone." People (in the US) seem to get this wrong most of the time, except for a few common phrases like "If I were you, ...".
2. The words "whilst," "amongst," and "amidst." I get that there is a certain history to these words, but I personally never use them as they seem like meaningless alterations. When I hear them, I roll my eyes, but I try not to judge too quickly.
3. "Irregardless". It's not a word.
4. "Could care less". An oldie but a goodie?
5. Overuse of commas. I don't like seeing them as strictly a way to introduce a pause in speech. Commas have specific grammatical purposes, and using them without such a purpose breaks my expectations as a reader.
6. Confusing "nauseous" and "nauseated".

I say "A part of me thinks [...]" (or "wishes" or "wants", etc) so often that it has started to seriously annoy me.

Homogeneous, meaning having a uniform composition. Hoe-moe-jee-nee-us (or hoe-muh- and/or -jee-nyus; point is, there's an ee sound before the last syllable). Saying homogenous (huh-mah-jeh-nus) in that sense is not only wrong but also means something else.

Sometimes it really annoys me if a perfect spot for a proper "whom" is missed. Even worse though is a misplaced "whom". Both instances are easy for me to spot because we decline pronouns quite a lot in German.

Edit: Sorry that's not a construction, so much as just an error. For constructions one thing that gets on my nerves is if you try to tell someone about your previous state of mind to clear up a misunderstanding like "I thought the water had boiled already" and then they say "no" to tell you that your assumption was incorrect. This is annoying because first of all the information they are conveing is already known to you by the time of this discussion and secondly in the grammatical sense they are actually disagreeing with your state of mind, not the content. I always have the urge to say: "Yes, actually, I'm telling you that's what I thought, you can't disagree with me about what I was thinking."

In English, I hate both "from where" and the rarer "from whence". I first found out about the words "whence", "whither", "thence" and "thither" (respectively meaning "from where, "towards where", "from there" and "towards there") while reading the Lord of the Rings in English. I found these were powerful words that could make many sentences shorter and clearer and that it was a shame they went out of popular use...

But then, I also heard "from whence", which struck me as far worse because it was redundant and stripped the word of its power. I first thought it was a mistake, but after seing it several times I looked up how it was meant to be used to see if I wasn't in the wrong and saw that while it had started as a mistake, it came into use several hundred years ago and was used by many famous classic authors, making it acceptable.

Imo, that's probably what killed these words. I guess it had the merit of being less easily misheard, but when "from whence" and "from where" mean the exact same thing, why bother remembering "whence"?

In my native language, French, I kinda dislike "C'est quoi ?" (Litt. "It's what ?", pronounced [sekwa] meaning "What is it ?). It's a vernacular expression often found incorrect... But I also kinda understand why it exists. The most correct way to ask "what is it" is "Qu'est-ce ?" ([kɛsə] or [kɛs]). It works well when written, but I guess being too short, it can be easily misheard. For example, "caisse" (a large box) is pronounced the exact same way. The other alternative, more common in oral speech is "Qu'est-ce que c'est ?" (litt. "What is it that it is ?"). It might seem too long, but it's pronounced [kɛskəse], which has the same number of syllables as "What is it". It is redundant tho, so I understand why "C'est quoi ?", which doesn't sound like anything else, rolls off the tongue and has two syllables is winning over, and will probably be the correct way in the future, but it still kinda sounds wrong to me.

ITT: people who understood the question and people who hate certain pronounciations for no reason.