Last week, Rihanna performed a song on Saturday Night Live decked out in some vaguely retro ’90s garb, surrounded by aquatic imagery, early ’90s memes and 3D effects. It was about as weird as it sounds, and it’s apparently called “seapunk,” a subgenre of “steampunk,” a subgenre of “fantasy” and so-on. All this would be fairly innocuous, except there apparently are a lot of seapunk aficionados out there, and they are blowing up the blogs with righteous blogdignation about how Rihanna has ruined the only thing that ever really mattered to them. So it goes, Rihanna. You swim with the seapunks, you get wet with angry blogs …