Just now I came to think of an incident a couple of weeks ago with a guy who really lacked social intelligence.
I went to a bar with my girlfriend and some friends, our friends went home but we stayed a while longer. This was a pretty loud place with music and dancefloor, but not quite a club. I went to the toilet for a few minutes and when I came back some dude was sitting next to my GF on the bench. He had his arm very loosely around her back just laying there, he basically said nothing and did nothing. I approached my GF, sat down on the other side and grabbed her around the back a little higher up. I thought maybe that was enough for the guy to take a hint, but his arm was still down on the seat around her back. He could easily see I had my arm around her, she was talking to me and we even made out. Still this socially retarded guy just sat there, he didn't even remove his arm and he hadn't said a single word yet. So I moved my hand down and gently pushed his arm back so he had to remove it, but did the guy take the hint then? No, this guy was still sitting there close to my GF. I gave it a couple more minutes just to see if he finally gets it on his own, but nope. So I leaned over, grabbed his attention and told him it was my girlfriend and suggested he try picking up one of the countless single chicks there instead. He didn't say much and it still took almost a minute after that before he went up and walked away.
I could have gotten him removed in less than 30 seconds, but I wanted to see just how socially incompetent this guy really was. My girlfriend clearly behaved in a way to signal her lack of interest (she's not the type who can be a bitch), but this guy didn't read that. I clearly marked her as mine by putting my arm around her more firmly than he even tried to, but this guy didn't read that. I made out with her, but this guy didn't read that. I removed his arm and still he didn't read that. Only when I directly told him it was my girlfriend did he read it, but even that took a little while.
If you wonder what a lack of social intelligence looks like, then this is it. Had he been socially intelligent he would have picked up on her disinterest before I was done on the toilet and moved on. Had he been just a little bit socially intelligent he would understand that she was a lot more into me when I sat down, made out with her and removed his arm. He was socially incompetent and he seemed very anxious and awkward.
I am absolutely certain this guy went home alone. His approach was extremely awkward and it's very unlikely it would have worked on any of the single girls either. But I could see him standing a chance if he could just learn some social skills, he wasn't bad looking.