Personally, probably 6 or 7 years ago when I had a gallstone attack in the middle of the night. Felt like a heart attack, but they didn't see anything when they hooked me up to take my pulse and listen to my breathing. The pain went away while they were there so I declined a ride to the hospital.
For someone else, it was last year. Wife and I were on our way home from the movies late at night when a couple cars wanted to race ahead of us after a turn - apparently they were clearing out the road for the guy on a motorcycle who proceeded to go flying past us at at least 90 mph. Unfortunately for him, that road has a gradual curve that you don't know about unless you've driven it before and he hit the curb. He went flying into the grass about 20 feet from the collision, and his bike was in pieces on the other side of the street. His "friends" and I went over to him to check and I was dialing 911 - they all got pissed and told me to hang up and he kept insisting he was fine because apparently he had done this before. Since I knew my wife was already on the phone with 911, I just listened to them and went on my merry way. Next thing we know there's multiple police sirens and their little mufflers racing down the street as they try to get away.
Oh, and the one before that a group of us were on the way home after a night at the Saucer. I-10 is about 15-30 feet below the access roads in downtown Houston, and this guy managed to come flying off an on-ramp onto the interstate. He rolled a few times in midair and crashed - a few of us got out to check on him and the girls called 911. The guy was completely drunk, and he fell out of the car I guess after it launched. Being drunk must have caused him to go limp because nothing was broken, and he was concerned about calling his ex-GF and letting her know what happened. Guess that's why he was drinking.