Alright, so long story short, I went over to a neighbor's house to help with some mechanical repairs on an ATV, and ended up meeting his son, who is roughly my age. I haven't lived at this residence for long, so I wasn't previously aware that he even existed.
At first the son seemed somewhat normal - A little absent minded, but no red flags were immediately raised. However, after spending another 10 minutes around his place, I quickly discovered that this kid is a FULL retard. Memory of a goldfish, attention span of a 3 year old, complete lack of social knowledge/understanding, and no learning/reasoning capability whatsoever. By my estimation he's about 22, has no driver's license (Not even a learners permit), and is still taking high school classes. Despite his assertion of knowing everyone in the neighborhood, his parents and sister all confirm that he has zero friends. I couldn't find a single reason to associate with this guy in any capacity, so I got the fuck out as quickly as I could.
Now, by some miracle, he managed to figure out where my house is, and he won't fucking leave me alone. 4-5 times per day he shows up asking me if I want to hang out, and at each instance I tell him I'm busy and can't do anything for the rest of the day. I ended up getting frustrated and giving the fucktard my cell number so he can call that and stop annoying my family multiple times per day, but it only took him about 2 days to lose the piece of paper (Which I had to write the number on, since he couldn't recall a simple 7 character sequence effectively enough to write it down himself, even after I recited it multiple times), and now he's back at the door. This has been going on for about 2 weeks now, and the breaking point for me was when he randomly walked into my house uninvited, claiming that he lost his keys and couldn't get into his own house. I almost fucking lost it, but then I realized that this imbecile standing in the middle of my living room really didn't know any better, and was completely incapable of comprehending the source of my anger and frustration. He's been around 7-8 times since then and won't fucking take the hint that I want nothing to do with someone who has an IQ that's literally half of my own.
So Totse, how the fuck do I deal with this situation? I don't want to tell him to go fuck himself, because the cognitively handicapped are highly unpredictable, and he may attempt to sabotage my brand new car which is sitting in the driveway. I'm on good terms with his parents, so I could talk to them, but I fear that may have the same effect as the first option. Burning down his house and/or killing him is also out of the question, as the connection would be too obvious. TBH I'm really not looking for criminal solutions such as framing him for possession of hard drugs or similar; I'd rather simply divert his attention to something other than... well, me.
If all else fails, I'm going to beat his head in with a baseball bat and deal with the murder charges.