A couple things that scare me:

1) Glow engines that start with a prop flip and no glow driver on (saw that). Be ready for them to start even if there's no glow driver. Keep the throttle at idle unless you're ready to go (kinda like "don't load the gun until you're ready to fire")

2) Folks at airfields pointing their 4-strokes AT ME while they start and run up the engines at the tables. That ticks me off... Heck, doesn't have to be a 4-stroke kicking a prop. Any plane could get outta hand and come at me.

Bgi,
I've had that happen. In defense of the parties involved, it was purely an accident. Buddy started his plane (pointed in a safe direction) and while moving around to the back of his plane tripped over a cord. Well, he bumped his throttle wide open and bumped the plane around towards me (wide open). Funny thing was that I was trying to get out of the way of the prop and try to catch the plane at the same time so it wouldn't hit my own planes!!!! lol. Luckily I caught the wing of the plane at the same time as he cut the throttle, so all ended well. But I can tell you that both him and I had a brown streak down the back of our pants after it was all over!!!!

point is, be prepared because anything can happen (and usually does) out at the field.