I get mildly irritated by people who get irritated by things that don't seem in the least irritating to me.

Having said that I feel an obligation to cite a couple of things I find irritating:

Anybody who says "in this day and age", implying that the calendar date has some relevance to the question of whether something is right or wrong.

Statements of the form "You make me angry".

People who say "in a perfect world" as a way of justifying adding to its imperfection.