People who park their car down their driveway so that it blocks the public sidewalk.
The police who drive by and see the same cars, and in some cases huge mobile homes, blocking the sidewalk day after day and do absolutely nothing even though there is a law against it.

Oh, that's two. Well here's a third:
People who block sidewalks, usually in cul-de-sacs,

with portable basketball hoops. Yes, they actually put the base of the huge basketball hoop onto the public sidewalk.