We had a guy (National-caliber driver) at a Cal Poly event show up with his daily driver 2002 on sticky tires. After watching him go around a 45mph (lightly banked) sweeper with the inside wheels 18" off the ground, we gave him his money back (no more runs). He really didn't think there was a problem (just lots of body roll).
Another scary sight was when one of our guys let his GF drive his DP Midget. The course had a turn-around on concrete (long, skinny course), and she jerked the wheel and the car came up on two wheels. Way up. From 200 yds away, you could see the entire under-side of the car. Remembering that a midget is under 5 feet wide, the right side of the car came a good two feet off the ground. And she held it there most of the way around the turn. Her boyfriend was going "NOOOOO!". The car had a cage, so I'm pretty sure he was worried about the car.