Yeah, when i was a younger English major, I was super insistent that everyone do things the right way. and while I can still be judge-y about that in certain contexts (formal writing and such), most of the time I don’t care. I became very Descriptivist about grammar sometime in grad school, which is funny because I was working in the Writing Center at the time, so I was paid to be the opposite of that.
The one that I always still do is British stule comma placement with quotations. American writing tends toward the oversimplified “always put the comma inside the quotations,” (as I just did for illustration), but I learned it as it only sneaks in if the thing in quotations is the main clause of the sentence (which is why that illustration took me extra work to do, and why I still felt like putting the comma after the parenthetical). I have had people get very mad at me about this.
I tend to start things with “I mean” too often.
I also notably don’t care about Oxford commas and find people who are very vocal about them annoying. Use them if you want; it’s fine either way. I could probably think of more of these, because I have sat in way too many editorial meetings about deciding the company style for these, but I mostly don’t care much.