The humor begins with the fact that this character is going to be uneducated about sex. You see, that will lead to awkwardness and if there is anything funnier than sex, it is awkward sex. So we know, simply because he says he'll need instructions, that he will have some hilarious troubles.
And then he can't even do that right! He gets the video wrong, and so he had even more awkward sex! I haven't laughed this hard since middle school when a teacher farted.
My goodness. How much lamer can you get than this comic? It's like a machine was told to look at all the previous xkcd comics and figure out how to make new ones, and it spit out "SEX PLUS VIDEO GAME. COMBINE THEM. THINK OF ONE IN TERMS OF THE OTHER." Does it matter that there couldn't even be a speedrun of sex? That it doesn't make sense as an idea?
I guess there will always be adults who are still amused by this sort of thing. Look: I have no problem with jokes about sex and stuff. It's just like reference-based humor: There's nothing wrong with making jokes that reference other works, and there's nothing wrong with making jokes about sex. The problem is when there is no real joke, and instead you are supposed to laugh merely because sex was brought up at all, and ha ha we are all still nervous about that.
That's really all this joke is: there's sort of a pun thing about video games and speed runs but it makes so little sense that i think we can all agree that the only reason anyone laughs at it is because: sex. and that is just lazy, when you get down to it.
as long as we're talking about speed runs, this comic always made me really happy.