Then the kid asks him if he'll ever "fuck him", and he says no. And then it's just subverted as he says he'll jerk off instead after a long pause.

Maybe you just don't like dry humor?

But to be fair, humor is subjective and maybe this one just isn't up your alley.

Yeah, if you already know that there's going to be a 'big twist', you'll most likely pay more attention and subconsciously (or even consciously) think of what the twist might be.