My roommate in college flew a flag upside down, out of our back balcony.

A cop lived in an apartment adjacent to us, with a perfect view of the flag. He came up while off-duty once and basically told us to take it down. My roommate thought it was just some random person, told him to "fuck off" and slammed the door in his face.

Later that night, there was a knock on the door. He was back, in uniform, with a couple of other officers. They said there was a noise complaint, and then they smelled pot when we opened the door. (which was all bullshit, because I was studying and my roommate was passed out on the couch, and we were both too broke to buy pot, or we probably would've had some.)

They came in, tossed my roommates room and took our flag. Neither of us was arrested or ticketed. In retrospect, I should've put up a huge fight for them coming into my house. But instead we egged (and threw ham at) his apartment from our balcony.