How is he pansexual?

The Avatar before him was Roku, not Kyoshi.

I would still watch whatever the fuck is described in the picture.

Minor corrections:

1. Aang may or may not be straight, we just know he came from a culture that didn't stigmatize homosexuality

2. Kyoshi was almost definitely bisexual. She seemed very attracted not only to Rangi but also to Yun, and furthermore we know that at some point in her life she had a child, which may have been adopted but was more likely just from a relationship after Rangi's death of natural causes (which would be like 150 years before Kyoshi's death)

3. As much as ignorant people (ignorant in-universe I mean) like to make fun of it, the Kyoshi Warrior uniform and makeup are not drag. There's no rule that men can't be Kyoshi Warriors and no alternate uniform guidelines for men. It's just a unisex uniform

4. Aang isn't vegan (unfortunately). He is okay with the exploitation of animals for products that don't directly require their deaths such as milk.