Parents

It's a fact of life that your parents will always do things that drive you crazy. They will always misunderstand and annoy you. They will sometimes make you feel like choosing the hardest wall in the house and banging your head into oblivion.
One of the problems with getting older is that you tend to realize that no matter how many times you argue, one day they'll be gone and you're going to miss them sorely.

Then you feel like a complete idiot.