It is not at all irrational or overboard to have a negative reaction to someone who is acting like an asshole. Your reaction to someone tearing through that sign was essentially "It's just a piece of paper, who cares?" If that's the basic minimum requirement when it comes to someone's property, then by all means, I hope you're not sleeping in your house when someone bulldozes it or blows it up. Just a house, right? WHOOPS DON'T HATE ON ME LMAO. It's not a false equivalency when I meet you halfway on your definition of what someone else's property means to them. Sure, it's not a thing to dwell on, but your inability to even show a modicum of respect shows that no one else is required to provide you the same service.

The dude who tackled through that sign had zero right to do so. Most people with less serious issues to deal with saw this and said "that's not cool." You came along and poo-poo'ed on everyone that had a problem with a clearly shitty thing to do to others that were doing nothing to the person who destroyed his/her sign.

Enjoy dealing with the real world as time goes by. When someone truly fucks up your day, remember the karma you put out into the real world as it bites you in the ass.