Walking the 100 lb dog while smoking and having to pick up a phone call, that's one of my life's little challenges.
Also, I like walking in crowded streets in Manhattan fast, passing people like a car on the highway passes other cars. Sometimes it requires some calculation and good timing.

hmmm - standing in the middle of the skytrain (rail car / subway) without holding onto something while maintaining balance and not looking weird :P

Adjusting my junk so everything is *just right* without anyone noticing.