It sounds like something Danny McBride would say, but it was made up by the actor who plays Jeremy, Jaxon Goldenberg.

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Joshua Encincias: In the opening scene, Jeremy say to Corey, “I don’t really feel like pretending to be best friends with an ugly-ass boy babysitter.” It cracked me up and I could hear Danny McBride saying that line. Did he come up with it?

David Gordon Green: It’s a perfect line and it’s not even in the script! I would say 90% of the humor in all of these movies is not scripted. Danny and I write these things pretty seriously, and the honest answer is lines like that come from an actor on set in the moment, which that one did. When you put the movie together you need this levity, I mean, I do. I like it, if it doesn’t betray the tone that you’re establishing. I really like infusing humor, not in a satirical nature, but in the Halloween movies, I feel like it has to be delivered by a smartass kid, a shit talking bully, or a bad joke from a character who isn’t funny. 

https://www.moviemaker.com/halloween-ends-director-david-gordon-green-on-killing-your-expectations/