Oh my god, I am embarrassed by you people. People are saying the guy is too stupid to sit at a bonfire and that he should have quit before helping his grandmother.

He didn't actually help his grandmother, he was probably going to the bathroom, came back, and saw this. Everyone makes the mistake of going AFK every once in a while, it's not a big deal. However, it's considered a dick move to not just wait for a minute or something, and in this case the host was coming right back. Obviously he has not obligation to wait, but it's something nice to do.

So, he decided to create this group to invite him to, calling him a dickbag. However, he used a made up story of his grandmother to make him feel bad, and called him an unrealistic insult. The message is clearly written in a way to be humorous.

You guys are all replying to this as if this is major hatemail and the guy is an idiot for thinking someone should wait on him when he's AFK, this is joke hatemail. It seems unlikely he'd even get mad enough to have rage over an AFK kill, there has to be reasons for it to build up. But he's basically saying that OP killed him when he was about to come right, and that's a dick move. But obviously there is no requirement to do so, and OP could not have known.