It's not fair to blame the hordes of bike commuters for the clusterfuck that is SE 21st & Division. With Ladd, Division, 21st, and 20th, it's a clusterfuck no matter what.
I would recommend a bat, when you stick your $40 umbrella in the spoke, it will shred it while throwing the rider in your direction. With a bat and a level swing you can take them off their seat and onto the ground without as much as a squeak. Success is yours and you save $40!
@BS. I like where you're coming from, but it can look rather suspect walking around with a baseball bat. I recommend a good solid heavy waling-stick/cane. Better cover, same results.