I've had a few, all on indoor tracks.
In more-or-less chronological order:
1) I was doing a warmup lap for a race at a particular bean - shaped circuit. I'm used to indoor karts having somewhat variable handling, but the one I had for this race was just evil. It would either understeer or oversteer wildly and on a whim, and with no apparent cause. It was so bad, I found it hard to aim the car at all. And this was just on the warmup lap. Anyway I started second on the grid, took first place at the start (I usually start well because I'm light), led the first lap, got to the left hander at the end of the fastest point of the circuit, tried to turn in to this corner (which was a flat out corner) and the steering wheel was jammed straight. I was stationary in the tyre wall before I'd stopped trying to turn the wheel and thought about braking perhaps. Turns out that the front right wheel had been loose, and once I got onto the straight, it came off the axle and jammed the steering. It couldn't fall off the car completely because it had wraparound bumpers. No pain though.
2) I was diving up the inside of someone when they closed the door a little too late. I had nowhere to go, so I braked, but his back bumper caught my front bumper, and pulled my bumper off. The bumper jammed under my kart lifting the front wheels off the ground, at which point of course I could no longer steer and I sent straight into the tyres on the outside of the corner.
3) I was racing a friend of mine and was getting better drive than him out of a hairpin. My car was slightly oversteery but controllable, he was suffering lots of understeer which was delaying him from getting on the throttle. I had him set up nicely going around this hairpin. I took a wide line in, got on the power early, got a bit of oversteer but kept the foot in, and aimed for the inside so that I could pass him on the next straight and get him on the entry to the next corner. He saw it coming and put his foot down despite his understeer. He ran out of track and bounced off the tyre wall, which meant he was suddently coming backwards towards me instead of vacating the track I was trying to use. I braked, was oversteering already so slid sideways into the back of him. It was the most painful kart accident we've both had. We broke both karts. My steering wasn't right after that and his throttle got jammed open.
4) Same circuit as above: We were racing and there was a girl with us who had never driven a kart before and was very slow. She was doing a good job of keeping out of everyone's way and I came up behind her on a long straight, which was about two and a half kart widths wide. She pulled to the left to let me past, so I aimed to the right and put my foot down. But she moved a bit too far left and clipped a tyre that was sticking out a bit with her front wheel. This madee her slow down suddenly basically bounced her sideways across the road right in front of me. I swerved to the right, missed her with my front wheels but caught her with my back wheel. There was a loud crack and a kart wheel came bouncing past me. It didn't feel like a big impact to me and I assumed it was her wheel but I thought I should stop and see if she was OK and thought the marshalls would probably want me to stop anyway, so I hit the brakes. The brakes on these karts only operate on the back wheels. Anyway, it turns out it was
my wheel that had come off, so when I hit the brakes, the kart of course turned sharply to the right, and I went into the tyre barrier
I've had a few spins as well. My most recent was at a 3 hour race at Buckmore (outdoor circuit), in the wet. It was the only time my team's kart spun in the event, and almost cost us a place, as it was 5 minutes from the flag.... fortunately it stayed on the tarmac and I could recover before the driver behind me could catch up. In the same race I also had a big scary moment in the fast right hand kink going down the hill, before the tighter left hander. It's the fastest point on the track, and this was when the track was still dry before the rain started. I lost the back end while riding the inside kerb. The kart recovered OK with a quarter turn of opposite lock but it felt like it was going to hurt if it did spin. Apparently the karts are doing about 65mph at that spot
)
). I mainly go to two kart-hire places near Perth
Cockburn (Pronounced Coburn 
) and Wanneroo kart circuits
Both of which are the largest outdoor tacks in Western Australia. The karts are very fast compared with standard hire karts, but unreliable
as I found out just before a hairpin after a very long stretch. My Brake wire suddenly snapped, and I was sent hurling across a very rocky/bushy shortcut through to the other side of the track, where my kart finally came to a halt. It was also the place where my friend managed to completely bowl-over two large safety barriers (the same Red and white ones used for standard roadworks 
