In cyberspace, "trolling" is when someone posts a deliberately controversial comment, not because they really wanted to say it but because they wanted to provoke an angry, emotional response from strangers -- kind of the online equivalent of insulting someone's girlfriend in a bar, or heckling a comedian, or snapping your towel at someone in the locker room.
So let's see what we have here: a mob of bicyclists, roving unpredictably and ignoring traffic laws, bringing drivers and bus-rides to a halt for ten to fifteen minutes. Everyone hates it except the people on bikes, who have a great time at everyone else's expense.
By nature, Critical Mass is confrontational, so as drivers sit and fume, tensions get higher and higher and higher. (Making matters worse, bicyclists' right of way is often poorly designed or abused.) As long as everyone keeps cool and minds their manners, it'll all pass. But one wrong move, and kaboom -- which is what happened this weekend in Seattle.