That's not an ad, that's genuine interaction. The poster is not an actor(or someone trying to act a role), not an algorythm, not a corporation, not a marketer or salesperson. We must learn to discern between stuff if we want to consider ourselves "real-worlders" or whatever. If you get the concepts mixed up in your mind then your discernment gets distorted and you start conflating what's authentic and what's artificial. That's why it shits in your head.

He doesn't want advertising in his life, but guy goes and immediately "shits in his head" using Bill Hicks of all people!

I think that's the joke.