95% of the time he plays the straight-man and then the other 5% of the time he behaves like an unhinged lunatic. It's the perfect recipe for cultivating an audience of viewers who love to torment him with his own words. After that it's just one step further to put words he didn't say into his mouth and see how he reacts to getting gaslit.
I make it sound like a cynical ploy but really this kind of thing is just intrinsically tied to Jerma's online personality. Lightning in a bottle. If you ask me the most impressive part's actually how he manages to stay in control of the situation and not get totally swallowed up by the increasingly bizzare behavior of his viewership.