Mobius: Knock Knock
Brad: Who’s there?
Mobius: Brad
Brad: Brad who?
Mobius: That’s show business
This is a bit of an old joke but the humour comes from two layers.
The first layer comes from the last two lines. Brad is a famous actor, so probably a household name. So the expectation is that nobody would ask who he was in the same way nobody would ask “Beyonce who?” But Hollywood is fickle and stars today can easily become forgotten tomorrow. Pretending not to know a celebrity is an insult that is associated with this nature of Hollywood. Hence the “That’s show business line” where the jokester acts like they’re reluctantly agreeing that the celebrity isn’t famous anymore. This is extra hurtful since the famous person is the one tricked into saying “…(their own name) who?”
The second layer comes from the expectation of the structure of a regular knock knock joke. Since this joke doesn’t follow that structure, it breaks expectations and creates humour.
Mainly it’s the first part though.
Did anything change after they became a big YouTube sponsor?