The worst encounter I had was not even a real encounter, but an act of vandalism / theft to my vehicle left at the trailhead. Had a window smashed, the stereo, CB radio, and a 4 D-cell mag lite stolen. I learned not to leave a CB in the open.
On the lighter side... a GPS would have saved the idiots from roaming in Blair Witch.
Something strange once was down the hill from a campsite, close to the creek, some trees had articles of clothing tied to them in a ritualistic manner. Looking more, the trees, each with 3 articles of clothes, were positioned in angles that made a 5 pointed star and all of the clothes were tied exactly the same fashion, with 5 folds/knots. We then joked about it humming the Dueling Banjo's tune.