Here are a few of them that come to mind:
- Okay, but faster next time.
- Let's have a race. You go first and I'll time you.
- Sure I'll follow, but let me get my parachute and sumo wrestler suit first.
- Ha! I did that without putting my foot down.
- Hey, looks like fun, but I just heard my Mom calling me.
- I wonder if you can do it this time with no hands.
- I know this dude with a unicycle and . . .
- I know this dude with a tandem and . . .
- Oh crap, I just got a fffffflllllllllaaaaaaaaaaaaaaaaaaaat. {Crunch . . . splash}.
If you have any others, please add them to the comment section.

