Hair Clippings, please fix in next Update or SOMETHING!

[Vurtney]

or mangle itself into a pixel ball

This exactly. Mesh collision and self collision on hair has a habit of "going bonkers". When the hair tries to settle down after movement it can do that in wildly differentiating results aka twitchy hair syndrome.

Tera fixed hair clipping in a clever manner. If your character equipped a long collar jacket for example, your characters long hair would show as tied up version of the same hair mesh.

Edit: I'm sure talented people at S-E could work something out eventually. I have gear sets with long collars and i have to adjust my hair style with that