Firecrackers, and the obvious - obnoxious dogs, heavy equiptment, small children in orange rain jackets and umbrellas, chainsaws, and yes, motorcross toys!
Some people who I don't know rode up into our yard the other day, and our dogs ran up to bark at them, like they bark at everyone who comes in the yard, and the lady's horse bucked her off. They were all pissy with us because our dogs scared their horse in my yard - they looked like they thought they would trail ride through our yard and it interupted their plans. This reaction infuriates me a little - I am often of the mind that it is the rider's responsibility to teach their horse not to be spooky, and control it if it does spook, not to yell at the outside factors (like little kids with umbrellas). May sound a bit demanding, but I have high expectations :)
Last night my husband and his friend were getting ready to go out on these really loud, dirt bikes and 4-wheelers. I was standing next to them with my boy when they took off, and my husband's non-horsey friend was worried about spooking the horse - he was surprised that he just stood there. My boy is a gem at home and on trails with my other horses. It is just events and new places with new horses that gets him all worked up.
"backed" and "broke to ride" to me both sound like ridden, but still maybe "green". I don't know technically though ?? :)