I am posting this since I know people here have been harassed and yelled at and what not. (I havent but them im a non-to-stable looking huge hairy guy – not your typical cyclist) but at least I havent heard of anyone trying to do anything like this.
I once hit a cinderblock that was hidden under a pile of yard waste (leaves) in a bike lane in Davis, CA. People just dump their green waste near the street, and some giant vacuum truck comes and sucks it up. Kind of a neat system, except for all the piles of crap in the bike lanes, and the asshole kids that hide bricks under said piles.
What exactly do they think they’ll accomplish? Fixing a flat is relatively cheap and easy. If this keeps up, you’re going to have militant bicyclists start tossing out homemade spike strips. Getting a car’s flat tire fixed is expensive and a pain.
Also, @dwillen, those cinderblocks are likely a deterrent for the people who like to drive cars through the piles and make a mess.