Clown Car doesn't always knock people over

[Walrus]

This might not be it, but when you drive the Clown Car or Segway, you don't need to hold the keys to move, it will go on its own. With Segways, I'm pretty sure by letting it coast into a person it will just harmlessly bump into them, the same may apply to Clown Cars.

I've noticed this happening pretty often and this seems like a good guess at what the problem is.