Responses I have used to reply to the "Get a real bike" moron:
Sorry I can't ride that slow.
Dude, I have 12 real bikes.
Nah, I don't really like paved roads all that much.
I like going around corners. Without paddling.
They sound too gay.
I would, but Pirate costumes make my ass look too big.
And my all time favorite, "Fuck off!"