A couple for us.
Late one night we pulled off for a break. We were in between Lakeview, Oregon and Winnemucca, NV, on a desolate stretch of highway about 100 miles from anywhere. We headed down a dirt road about 1/2 mile off the highway to sleep for the night (a spot I'd used before). Kids tucked in and I was just drifting off to sleep when I heard a vehicle on the highway -- loud sound of mud tires and a v-8 engine was easy to hear due to the lack of any trees or anything between us and the highway. Heard the vehicle slow down and stop, quiet for a minute, and then heard it coming down the dirt road until it stopped right next to our trailer. Loud death metal playing and several male voices. It drove around the trailer a couple times, I heard a door open and close and footsteps walking around, but no more voices. Don't know how long they were parked there walking around -- probably 30 seconds to take a leak or something, but seemed like forever, and then the truck finally pulled away. Who knows, we were probably just parked in their drinkin' spot or something, but I was wide awake after that!
Another time, also boondocking in the mountains of So. Oregon. After sleeping the night, I noticed something off in the trees and down the hill a little bit. I started to walk down there and suddenly noticed 5 or 6 guys sitting there with eyes on me. What I saw was an edge of a large tarp structure that housed I don't know how many people.
I made eye contact with one of the guys and he said "just makin' sure you aren't coming down to steal any of our stuff ...", which I found rather ironic, since I had $50k worth of stuff parked next to their $20 shelter! But it was creepy to know that people had been walking around our campsite and potentially watching us all night and we didn't even know it!