People can't seem to resist stopping to pet my dog when we're out on walks, whether or not I want them to. I've had people come up from behind us while Ranger is in a "sit-stay" and start petting him before I've even seen them!
My next door neighbour's have two young kids and they've taught their children how to approach a dog. It's great! They come over sometimes to help me "brush" Ranger and these kids have more dog-smarts at 2 and 4 than most adults I've run into.
The worst was my boyfriend's step-sister. I was sitting on the ground with Ranger and she came up to us in my blind spot(didn't even see her), SQUEALED, then threw both arms around his neck! I had only had him for about 15 days and had no idea how he was going to react. Luckily he was fine. In fact, I think I reacted worse than him!