Everyone has a few pet grammatical peeves.
Some have become so common that they are now acceptable: like split infinitives or using “they” to refer to a singular object.
An article from BuzzFeed offers us some excellent examples.
Here is a sampler:
Split infinitive: You need to really focus.
Using “they” to refer to a singular object: That person knew what they were doing.
The dangling participle: Walking along, cars whizzed by.
Discord between subject and verb: There’s towels in the closet.
Confusing “lay” and “lie:” I’m going to lay down.
Double negatives: I didn’t do nothing.
For your further edification, I can tell you that all but the first three were flagged by the Microsoft Word Grammar Check.