What is the poper nudity at home?

Casual attire at home is whatever everyone is comfortable with, including being naked. There is no reason why you shouldn't be naked if the other members of the household are OK with it. Put something on when your girlfriend comes over for her comfort, but don't let her tell you what you should do in your own home with your own family. If they run around in bunny suits over at her place, that's their business.