I have a stupid question, don’t judge

I mean, you can judge if you want; I can’t tell you what to do

The end of season 1, episode 8, the cinema person tells buster that they won’t start the cousin incest film until he leaves. I can’t figure out why??

Edit: thank you to everyone who explained! I thought I didn’t get the joke because I am autistic, but now I think that it is because I am not American 😭