I’m hard-pressed to pick a favorite part, but the “member of the public” screaming “COME ON!” through the window in between bites of his donut is pretty damn funny. Same for when the guy rips off some paper towels and then starts drawing a diagram on them.
This might be one of my favorite things ever. Love it. And nothing beats the lady screaming as she lowers a lit flame towards the coffee, though the public screaming their disappointment is definitely great too.