(My rule for this list is: There are things I've witnessed first-hand. Not heard about - actually seen directly.)
You see a bunch of guys with low-slung pants, huddled together on a curb, arms over each others' shoulders, grinning like mad, and waving back and forth like a church choir, while a BMW cruises slowly past them, turns around, and cruises past again, over and over. There is a big digital SLR camera suction-cupped to the hood of the car. Nearby, a boombox is playing a rap song.
You're arriving home, at night. Some kind of argument is happening in the apartment above the convenience store on the corner. The lights are off, but you can hear a couple of men, yelling at each other in farsi, plus various thuds and crashes, getting louder and louder. Suddenly a small metal chair comes crashing out the window and tumbles into the street. Everything goes quiet. You shrug, and go inside.
A mail truck stops at the intersection and the worker gets out to deliver a package. A man sprints over from across the street, shatters the passenger-side window with his jacketed elbow, and takes off with the box left on the dashboard. The thief vanishes around the corner and down the block. The postal worker spends the next two hours standing there while the police take a report, and the mail is transferred to a new truck.
Half a block from your front door, you find a pile of small personal possessions heaped on the sidewalk. It's the discards from a recent theft, chucked out a car window. You go through the bag and discover a couple USB drives, a passport, two phones, a stack of checkbooks in another name, some ADD medication from a foreign country, and a bunch of scribbled notes about grow farms and cannabis supplements. The victim is a pothead college student, abusing generic Adderall and mooching off his parents. But, you feel sorry for him, so you track him down on Facebook and reunite him with his crap.
At a long stoplight, the teenager in the car ahead of you finishes his bottle of iced tea, then opens his car door and casually sets the bottle down in the street. He sees your disapproving expression in his rear-view mirror, and when the light turns green he flips you off and races away, dodging recklessly between cars.
You hear a strange "thup thup thup thup" sound out in the street, then a couple of men yelling "Whoooaaah!" You walk outside and see a young man crouched behind the open door of his SUV. He has a paintball gun resting on the windowsill, with a hopper full of paintballs attached to it. He's looking down the street and yelling at the passenger in his car:
"They rain out of air, man! We got them! They out of air!"
You look down the street and see busted paintballs crushed into the pavement, and some fresh tire marks. The men in the SUV close their doors and drive off. 30 seconds later, a police cruiser shoots around the corner, in pursuit of the SUV.
On your way home from work, you have to take the long way around to your house, because the police have cordoned off an entire street with yellow scene tape. Behind the tape you see three police cars and a small crowd of bystanders.
On the Bart train, a man sitting across from you stops checking his phone, leans over, and vomits a huge puddle onto the floor between his legs. The train brakes to a stop, causing the vomit to snake down the aisle towards the doors, which open. Without a word, the man bolts out, slipping in the puddle as he goes. But he left his phone. So you take a picture of the vomit with it, and text it to the first person in the contact list, with the message "you left this phone and this vomit at MacArthur Bart." You hand the phone to the MacArthur clerk on the way out.
You arrive home to discover a huge crowd walking down the middle of the street holding banners and chanting. It's a lovely evening for a walk, so you join up. You go a couple of miles, then ranks of riot police show up and start cornering the crowd. Just before they start firing teargas grenades, you decide to walk back home.
You're inside reading. In the distance, not too far away, you hear six gunshots fired in rapid succession followed by a car driving off. Then you hear someone yelling "I’ve been hit!" "Where?" "I dunno it just hurts! Let’s get out of here!" 45 seconds later you hear the sound of sirens. You walk outside a bit later to find three police cars. A nearby officer holds up a plastic bag into which he has placed a used shell casing, inspecting it with his flashlight.
You're making your way around the lake on a bicycle. The pathway opens up into one of the patio areas, and you spot half-a-dozen fellow cyclists, resting with their bikes leaned up against the stone bench, drinking beers. The bicycles are all tiny - less than two feet tall - with tiny seats and handlebars. One of them has a toaster on skateboard wheels tied to it by the cord, making a "trailer" just large enough for one beer. "We used to ride Harleys," explains the rough-looking guy on the end, "but now we take these around the lake. This is more fun." Then he burps loudly.
You're out with a few friends by the lakeshore. Ahead you see the bird-feeding area. As you approach, you spot two fat rabbits inside, darting around from one hiding place to the next, being chased by a woman and a man carrying a cardboard box. "They're obviously domestic rabbits that someone abandoned here," the woman explains. "We're trying to take them to the animal shelter. Will you help?" So you and your friends join a crowd of people, chasing rabbits around by the lake. 15 minutes later they're both safely in the cardboard box.
You look out your window and see a man walking slowly down the sidewalk. There is something odd about his gait. He stops at a telephone pole, inspects it closely, then raises a tool in his hand up near a box on the pole and begins pulling at something. His other hand moves to his pocket, and then he proceeds to the next telephone pole, repeating the move.
You walk outside, wondering what in the world he is doing. You get about five feet away and see that the man has a pair of pliers, and is patiently removing staples from the telephone pole, one at a time. He glances at you and says, in a strained voice, "You're just gonna have to let me do this." You realize immediately that he is an insane street person, passing his time this way in order to prevent himself from doing something much worse, to himself or to someone else.
"Hey, no worries; you just keep on doing what you need to do," you say, and walk casually back inside.
You've parked your car and are about to walk across the street to your house. Suddenly the noise of sirens is all around you. 20 yards away, you see a beat-up sports car shoot around the corner. As it approaches you see a young man at the wheel with an expression halfway between anger and panic. A cop on a motorcycle is only a few feet behind in hot pursuit. They both roar down the street and around the next corner, with the cop leaning way into the turns, lights blazing. A police SUV zig-zags heavily behind them, lights also blazing. A few seconds after that you see a helicopter plunge diagonally across the intersection, tracking the action on the ground. The helicopter and sirens orbit your block for the next 20 minutes.
You hear some shouting, and walk outside to investigate. A car is stopped directly in front of the house, blocking your driveway. Two police cars are blocking it on both sides. Three young men are sitting on the sidewalk, next to one cop, while another cop searches through the car with a flashlight. Another man is standing nearby, yelling "police harassment!" over and over, mixed into a stream of random swearing.
"Go about your business," says one of the men on the sidewalk.
"You know this guy?" asks a cop.
"Yeah, we've seen him around," says the man. "He gets like this when he's drunk."
Eventually the fourth man wanders up the street, still yelling from a distance, and the cop completes his search of the car. He comes up with a couple of baby bottles with rubber nipples, filled with bright red liquid. Cough syrup.
"I probably shouldn't ask if you have a prescription for this, huh," says the cop.
"Nah, man. Actually you can just pour it out if you want."
The young men and the cops have a brief discussion and everyone departs, but just before the young men drive away, the fourth man comes back down the street and yells at them. "Police harassment, am I right? Man, I hate the pigs! Just a bunch of ... " He is still swearing when the car pulls away, leaving him alone.
. . .
There are definitely more I'm forgetting...