Look, we all know its just a matter of time before self-driving robo-cars are everywhere. We can either piss and moan about how dehumanizing it'll be and how driving will be dead, or we can have some fun messing with them. I'm on the side of fun.
Self-driving cars are, essentially, robots who have the unenviable job of hauling our asses around. Now, what I'm advocating here isn't actual hacking to be destructive (i.e. no GPS hacking to drive cars into petting zoos or kitten aquariums), I'm more just speculating what sorts of goofy, stupid things will be possible once these self-driving cars are common. I'm not actually endorsing anything, so if anyone gets themselves run over in a decade or so, don't come looking for me. I'll probably be in a cult or too obese to leave my van or something, anyway.
I'm assuming a few things now about these future self-driving cars: first, they'll be based on the ones we're seeing now technologically, and second, laws will be in place to let them drive on their own for some things, like in those self-parking demonstrations we've seen. Also, for all of these, I'm assuming they'd be done on cars that are either unoccupied or occupied with owners too drunk or asleep to yell at you to get the fuck away, you idiot kids.
Aside from creating vast gangs of desperate, hungry valets, cars that park and drive on their own, unmanned, will be ripe for screwing with, like how as a kid you played cruel games on a drunk bison. Here's some ideas I came up with — please feel free to add to the list in the comments!
1. Car Herding!
This one, like most of these, uses the collision avoidance sensors and cameras almost every autonomous car will have. And while I can't be certain this (or any of these) will work, it might!
For this one, you'll need a group of friends, say six or so. You'll spot an innocent robot car hunting around for a parking place, and then surround it in a loose, wide, circle. Various members of the group will approach the car's hazard-avoidance sensors (usually at the corners and central front and rear) to force the car to stop and/or change direction to avoid you. I was in a prototype Nissan in Japan that did just this.
If everyone works together, you should be able to "herd" the car at low speed in any direction you'd want, sort of like how you could herd a nervous livestock animal or something. I bet it'll be fun. I don't think this would ever be a popular way to steal a car because it seems really, really slow.
2. Instant Unwanted Autocross!
This one takes just a bit more advanced planning, and a whole bunch of cones. You see a car heading your way, so you set up a quick autocross or slalom course with the cones, and force the car into it. You'll probably have to use the herding techniques to get it into the coned-off area, but once it's in, if you set your cones right, the car's sensors will force it to navigate the autocross track as best it can.
Set one up in a parking lot and run multiple cars through, while taking wagers on times for some serious fun!
3. Roller Skiiing!
This one's easy. Put on roller skates, grab a plunger, wait for a car to come by, looking for a spot in a parking garage. When it's close, jam the plunger on the car and hold on for one hell of a probably just-above-walking-pace ride!
4. Auto Sumo!
This one may be tricky, but should be worth it. You'll need a nice big empty parking lot or something and two autonomous cars. Herd them close to each other, then enclose them in a ring of cones. from there, try and get them to circle and chase and go after each other by blocking/revealing the collision sensors. At some point, the cars should start reacting to each other. Each car should have a GPS destination set just beyond the other car, so they are forced to navigate past one another.
Winner is the one who forces the opponent out of the ring first!
5. The Trap!
This one's also pretty straightforward: track a car as it's driving, then surround it with objects (front first, so it stops) so that you've trapped it!
After that, I guess you can stab it with your spear, carry it back to your village, and have a huge potlatch! Who's the Big Man now?