This is a fascinating thread!
Not a backcountry experience but a creepy one none the less. 35 years ago, I was perched in a valley treestand, during archery season, in a tract of hardwoods near my parents' home. This tract bordered on of the state's largest mental health hospitals. Growing up in the area, us kids would build forts, etc in the woods surrounding the hospital and occasionally run into patients who wandered off the hospital property, as it had no fences. Most of the folks were harmless but this facility did house a number of folks who were truly disturbed.
Anyway, getting back to being perched in the treestand one evening, I got that strange sensation of being watched. That feeling proved to be correct as I saw a figure moving through some thick brush on the hillside about 100 yards in front of me. Thinking it to be just be one of the 'wanderers', I didn't pay it any mind for a few minutes. Upon just beginning to relax, I was again overwhelmed with that feeling. Out of the corner of my eye, I saw a man walking on the storm sewer cut behind me about 60 yards. He was wearing sweatpants (typical of the hospital patients) and a blue flannel button-down top. I wasn't sure if he had seen me or not but I had a feeling that this man wasn't one of the harmless patients, as he began to pace back and forth along a 30 yard length of the cut, speaking and cursing loudly to no one, balling his fists, and hissing/spitting like a cat.
It was getting close to sundown so I though it best to climb down and slip out of the woods, knowing I had a steep hill climb back to the house and didn't want to alert this man to my presence, as he was between me and my way out. I waited until he had walked in the direction away from me, lowered my bow and pack, climbed down, and started to do a long loop up and slightly around the hill in front of me. I dropped out of the woods against a pasture field, crested a short rise, and was surprised by the same man sitting on a fallen tree, massaging his bare feet (with no shoes anywhere in sight!). I remember thinking 'there's no way that guy could get here before I did!' I was stuck and had no choice but to go by him. As I approached him, he looked up at me with eyes like Vincent D'Onofrio's character in the bathroom scene in Full Metal Jacket. As casually as I could, I said hello and kept walking by. As I passed, he asked me if I was in the Army and 'on maneuvers'. I said 'no' and kept on walking. Behind me, he hissed loudly and that put a hop in my step. I went about 100 yards before looking back behind me. The man was gone from the fallen tree although I didn't know which direction he had gone. I double timed it up the hill and out of the woods towards home!
Spooked me enough that I didn't go back there anymore that year and, not long after, the land was sold and a housing development sprouted up. While the man may have been harmless, his actions and me being an 18 year old kid at the time, still make the hair stand up on my arms as I type this!