[To him, knowing a person's name makes them familiar enough. Adding a -kun or a -san or whatever just seems confusing. Plus he wouldn't know when to use which honorific and... Yeah. He'll stick with Hinata.]

That's because it is painful. It's even worse when you first arrive and you keep forgetting about them.

[Then you end up leaning on things and, oh right, the wings. Ow.]

But like I said, you get used to them. They toughen up pretty quickly so you don't have to worry about what you're doing with them all the time.