Old-Timey Misogynist: Women should not ride bicycles. It disrupts the menses!
You: Whoa, haha! Um, okay, very interesting! [can’t wait to go tell Tumblr about this]
or
Child: I’m a demon. You’re a turtle. Demons beat turtles, die die die!
You: Oh! Hahahaha that’s great, sure.
Like that. Practice your condescending laugh.