Why Self-Amusement is Crucial in Pick Up
SELF-AMUSEMENT IS CRUCIAL.
When you're working hard to entertain someone else in the room, who do you think has greater status? The guy who's sweating to provide the other enjoyment or the one who is actually receiving the enjoyment? By providing entertainment you're demonstrating high interest in the other person and that's a problem. In PU you want to start off with minimum interest (that's why we neg) and even in the first stage of a relationship you still want to maintain a low-level of interest (because she didn't earn your high interest yet).

If you're going to be entertaining you need to calibrate by doing things that lower you interest in her. The Main Thing here is Self-Amusement. You're being entertaining because it's fun for you not because you want her to feel good. Because it makes you feel good. She happens to be there to hear your self-entertainment. This strongly decreases the interest you've shown her by being so entertaining and raises your status back up.

To show that you're engaging in Self-Amusement you need to show that you're obviously enjoying yourself. Smile, laugh and have a blast for real.

IF YOU'RE NOT HAVING FUN.
If she sees that you're not enjoying the interaction she will wonder why you are there in the first place. Human beings enter social interactions because they enjoy them or because they are trying to get something out of the person (they have an agenda). Now, if you're not in the social interaction because you're having a good time she will think that you're in the social interaction because you are trying to get something from her (sex or something else). And hidden agendas are creepy. By not showing that you're enjoying yourself (taking value from the interaction) it will look like the only thing you care about is to try to get into her pants and that's a needy, unattractive mindset.

I will agree.

You could say the exact same thing, but self amusement and trying to entertain will have a totally different type of vibe to it.