I think I have had time to calm down when thinking about how Yiffany came to be. And I'm still angry, but more so at the adults in her life and how she came to be rather than who she is. Suppose they had made it so that Yiffany didn't hate her name, her parents, the circumstances of her life, and tried hard to put some bullshit positive spin on her existence by making Yiffany herself happy about it or some shit. In that case, I don't think I'd have ever really come back to read the rest of the comic.
But seeing that panel of Yiffany yelling "Fuck you!" to the rest of them when Vriska whisks them away to better opportunities reinvigorated in me the need to read Homestuck. And I think this website, as well as the few dialogue options you can read when you try to take her name, also vindicates the reader. Yiffany IS a terrible name, and the people who gave her the name ARE terrible, and no amount of wishy washy "I-it was a terrible writing decision on purpose!" will ever really abate the rightful anger people felt when reading it.
Yiffy's anger, in a way, is also MY anger, and I want to see that feral little gremlin child do great things.