we had a similar event happen to us, some random kid all of the sudden was in our circle smoking, we told him it was PCP joking, but he was pretty wasted i think he thought we were serious. so he then proceeded to take off his shirt and sit there with his had down his pants. We got his drunk ass up off the couch and told him he had to leave. 5 minutes later we open the door and the kid is perched up on our front porch so we told him to get out of here.
then he proceeded to walk up the street, fell into someones yard, security guards saw him, called the cops and ambulance. he got his stomach pumped and thats the last we saw of him.
tl;dr;
Similar story to OP, we discovered no one knew this random kid in our house, told him he was smoking PCP and he freaked out, left, passed out in someones yard and got picked up by the ambulence.