Mansplaining—there are few things more annoying. No, not all men do it, and no, it's not every time a man explains something to a woman. Mansplaining is when a man specifically tells a woman something she already knows, something that is maybe even her area of expertise, because he assumes he knows better.
For example, I once overheard a customer at a Filipino restaurant explain to the native Filipino waitress, who spoke Tagalog, that she was pronouncing a dish wrong. How she didn't hit him over the head with a plate, I'll never know.