People who ask for advice, then ignore it. I'm not saying people should always adhere to advice, but when someone has difficulty in a situation, asks for advice, then pursues the dumbest option available to them, it's a bit silly.
This typically revolves around people asking about relationship advice, as relationships are the most commond scenario for people acting like complete morons.
This is why I try to only have single friends.
And for that matter, people who define themselves by their relationships. They grind my gears. Because they often behave in the aforementioned idiocy more frequently than others.