Alright, if you had to pick one, which should be addressed first?

Bicyclists on sidewalks
Bicyclists using a cellphone while riding
Bicyclists carrying umbrellas while riding.

:-)

Or my particular favorite, when they do ride on the sidewalk, the incessant pinging of their little bells from behind to tell you, the pedestrian on the same sidewalk, to move. One guess how often that happens when I am involved. :-)