While my choice for the most annoying grammatical error is the misplacement of an apostrophe in "its," for my brother the writing teacher the greatest irritant is the dangling participle. I have one for him: the most awesomely dangling participle I've ever seen, one that dangles over a precipice more dramatically than any dramatic scene in the movie in whose review it occurs, The Force Awakens. (Or so I presume. I still haven't seen it.)
The dangle occurs in a paragraph discussing Leia and her place in the Star Wars universe, and it reads as follows:
"Like many straight men of my generation, she will always have a special place in my heart."
Wow; just - wow. And the author of this thing is an English don at the University of London. Yet all he can say when called on it in the comments section is, "Not a very well-made sentence that, no. I concede it." Not very well made? You'd have a challenge finding a worse-made sentence by a university English teacher. I'm sure you could find one, but I wouldn't envy you the task.
You may not want to read the review. Roberts doesn't believe in withholding spoilers, and he begins by lecturing you on why you don't like that, getting the motivations entirely wrong in a condescending way. He also writes as if he's discovered something new in the tired old phenomenon of the action-adventure movie which is nothing but its own trailer with padding added between the exciting bits. He also gets the business about fathers and sons, and the original trilogy's treatment of them, wrong in more ways than I have time or interest in writing about. There you go.