I have several...
BB Owen DGC (Dallas), circa 2009 - The group I used to play with would play every saturday morning somewhere 8am. This particular week I decided to sleep in. Glad I did. They were the first ones to the course that day and found a dead guy near #18's basket. gun next to him and bullet hole in his stomach. He had committed suicide sometime overnight right by the basket. They were the ones that called 911 and reported it.
BB Owen DGC (Dallas), circa 2009 - We were playing at BBO and threw our drives on #9 (looks like it is #12 now) and my turnover shot turned way over and into the thick woods on the right. We all started looking for my disc and one of my friends calls out to us that we don't want to go any further in there. We asked why and he said just take my word for it. Somehow I found my disc on the way out of the woods...then he tells us the reason. He had come up on a homeless guy, laying on his back on the ground, completely naked except for socks. masturbating. Apparently just going at it. Glad I missed that.
Lake Arrowhead State Park DGC - Wichita Falls, TX - circa 2003 - We were camping there and playing the course. Came up to our drives which were all pretty close to the basket (course was pretty short). As we get near the basket we see something under it. Get a little closer and we see it is a baby rattle snake, right next to the pole. We considered all our putts "gimmes" and got out of there.
Fritz Park DGC - Irving TX - a couple weeks ago - Our group came up to the tee on #16. There was a guy in the fairway dressed up as a samurai and swinging an imaginary sword through the air. He was doing really crazy things. A couple guys yelled at him that we were about to be throwing towards him and to watch out. He ignored them. I walked toward him to try to calmly tell him what was going on. He looked at me (looked completely insane) and started talking gibberish about being some superhero killer and he didn't care that we had guns, he could defend against anything (we didnt have any guns). He then got on the ground and started punching it so hard I'm surprised he didnt break his fingers. We just went around him and made up a temp tee box.
Not really a horror story but one of the weirdest things I ever saw playing:
Lake Park DGC (Now Old Man DGC) - Lewisville TX - circa 2004 - There was a dude playing the entire disc golf course...backwards...using a golf club...hitting tennis balls. The dude was a little "special" I think.