The most interesting part is often the moment of surprise. For example, when someone gets into the wrong car by mistake and then realizes it. It's that sudden shock and embarrassment that makes it funny.
I once saw a guy car hopping in a hurry. He thought he was getting into his own car which was parked among many similar - looking ones. As he opened the door and sat down, he realized it was not his. The look on his face was priceless when the actual owner showed up a moment later.
Once, my friend and I were driving in the countryside. A huge deer suddenly jumped in front of the car. My friend slammed on the brakes and we both screamed. But then the deer just stared at us for a while and casually walked away. It was terrifying at first but then we couldn't stop laughing at how silly it all was.
I know a story where a man was tired of his neighbor's extremely loud car stereo. He got a bunch of helium balloons. He then tied them to the neighbor's car antenna when the neighbor was inside his house. When the neighbor came out and started his car with the loud stereo, the balloons were bouncing all over the place and blocking his view. He had to stop the car and get out to remove them. It was quite a funny sight, and he was a bit more cautious about his stereo volume after that.
One story I heard was about a neighbor who always blasted his car stereo really loud early in the morning. One day, another neighbor parked his old, rickety truck right next to the loud car. The truck had a really squeaky fan belt. Every time the loud car owner started his engine, the neighbor would start the truck and let it idle. The squeaking was so annoying that it made it impossible for the loud car guy to enjoy his own music. Eventually, he stopped playing his stereo so loud in the morning.
I have a funny story too. A guy went to a used car lot. He saw a car that looked really cool. When he asked about the price, the dealer said it was very cheap because it was haunted. The buyer thought it was a joke at first, but the dealer was dead serious. In the end, the buyer walked away, of course.
Once, I was on a road trip with my friends. We got lost in the middle of nowhere. Instead of panicking, we started making up a story about being on an alien planet. Every strange noise the car made became part of the story. It was so much fun that we ended up not caring about being lost at all.
Once I got my first car, a really old beat - up sedan. The first time I drove it to work, the horn started blaring randomly in the middle of traffic. I had no idea how to stop it. I was so embarrassed as people stared at me, but it turned out a wire had just come loose. I just laughed it off after I fixed it.
I remember a long car ride where we were all singing along to some old songs. My friend, who thought he was a great singer, was really off - key but didn't realize it. He was belting out the lyrics at the top of his lungs. We all started laughing so hard that we could barely breathe. But he just kept on singing, completely oblivious to how funny he sounded. It was a great bonding moment during that long ride.
Once, a guy was driving and his dog suddenly jumped onto the steering wheel. The car swerved into a field full of hay bales. Instead of getting angry, the driver just laughed as his dog looked so confused. And the car just had a few scratches from the hay.