In retrospect, was probably the Battle of Seattle in 1999. Not that I wasn't aware of the issues before, but that really ripped off the mask to show me that the U.S. is fundamentally rotten at its core: The police are not the good guys, they don't serve and protect, they are there to visit violence on the enemies of capital. And if innocent people in their homes or going to work get caught up and harmed, fuck 'em, they're not wealthy enough to matter. The media will flat-out lie to maintain the good-cops-vs.-evil-protesters narrative. Our leaders will eagerly sell out American citizens to the interests of global capital, with only lip service to democratic traditions. And Americans are too disengaged to really question any of it.
For me, it provided the keys to understanding the events since, from Bush v. Gore to today. At least now the rot has become so obvious that the younger generations are forced to notice.
It was the result of anti-World Trade Organization protests organized at the group's gathering in Seattle in 1999. Basically, the police see protesters axiomatically as bad, so they showed up in riot gear and started a riot. The media reported it as violent protestors, despite some of the people who just lived nearby and were trying to get to and from work getting caught up, kettled, teargassed, and beaten alongside protesters. I wasn't there, but the Internet had become a thing, and IndyMedia.org had lots of first-person coverage. It was the same pattern we've seen ever since cell phones with cameras have become ubiquitous: The video shows that the cops get violent and then lie about it.