Friend of mine dropped this awful Knock Knock joke on me

Friend of mine dropped this awful Knock Knock joke on me

A friend of mine walked up to me the other day and proceeded to begin the conversation with this:

Knock knock.
Who's there?
Barack Obama.
Barack Obama who?
Barack Obama who? Are you kidding me? He's the president! Do you live under a fucking rock?

And then he stormed off. Quite possibly the worst joke that I ever laughed at!