I used to be able to hoot like a owl through my cupped hands. Also, I could fall from trees and remain unscathed. Neither are possible anymore
I could ride no-handed too, which I can just about manage but I think that is more a geometry thing than an Ambrose-failing (correct me if I'm wrong, I probably am...) I could never wheelie but used to be able to do a mean stoppie, alas no more.
Biggest regret though- I could never get the fingers in the mouth whistle thing. Uber loud and piercing, but all I got was spit and a hiss of warm air.