-People who beat things to death over and over and over and over. Especially when they were never funny or clever in the first place. This applies in real life and online.
-Not knowing you're/your and to/too/two. You are stupid if you don't know the differences.
-Spelling definitely as definately/defiantly/defanatly/any variation.
-My mom's tendency to lie all the time, or even worse when she acts like something doesn't bother her and then later will throw it in my face. HATE that.
-People who audibly gulp their drinks or slurp soup.
-Vegetarians/vegans who preach about eating meat and animal products and how wrong it is. I have nothing against vegetarians whatsoever, I just hate the ones who preach. I don't care about your eating habits, STFU about mine.