Mine is billy cart accident.
I and my 2 bros (they are12 and 11 years old...)
i am 13...
We all wanted to go on the same billy cart so we added a trailer to our already cool billy cart it looked like kr4p but it went fast!
The extra weight of my 2 bros in the back made us brake the brake 0_o
Snap the front axel all while we were doing about 30-45km/an hour
We hit the a bump (Coz i couldnt steer) then us and the billy cart (all of us still in the billy cart) were throwen into a tree smack bang in the middle of it!
Out of all of it...
my 11 year old bro escaped with only 2 minor scratches.
12 year old bro almost had his ear removed from his head (very deep cut)
and me, the unlucky one i was unconcious for about 30 mins.
had ripped my thigh open, my head was all red from blood and hand was hurting like hell (It had a stick about 1 cm deep)
So yeh...
Guess what i have no scares whatsoever!
I am so lucky

In future i will never ride a billy cart with 3 people again (I am going to drive 5 people in a billy cart tomorrow, J/K)