Dress in all yellow; sweatshirt and sweat pants are probably the easiest!
With black felt, or any other similar fabric, make two strips that resemble
tire tracks, each about a foot wide is good. Make each of them long enough
to fit over the front of the body, from one side to the other. Use hot glue to
stick the "tire tracks", one along the top of the chest, and the other around the
knees (you'll have to cut this one in half for walking). Basically, place them wherever it looks like you've been "run over"!
Thanks to Jen for this unique idea!
We put black paint on a spare car tire and rolled it across yellow sweats. We also made a street sign that said "slow speed bump"and my son carried it.
Thanks to an anonymous submitter for this additional idea.