Waxing of upper lip or bikini zone is just some of the women's beauty rituals that they won't do in front of a man. When women are beside their partners, they try to make themselves look the best and don't do many things that could make them look bad.
Men, on the other hand, won't pay so much attention to these things and they'll be 'relaxed' as soon as they set foot into their living space. Women will, therefore, use the time when they are alone.
Hairs: Even though many couples don't hide anything they do from their partners, women will rather leave 'dirty work' for a time when they are alone at home.
Waxing of upper lip or bikini zone is just some of the women's beauty rituals that they won't do in front of a man. They will watch the film or series that you agreed to watch together.
She has extra time and her curiosity makes her see the next episode of the series that you watch together. Or she watches a TV program 'for her pleasure', for which you don't even think she would be interested in. Documentaries on killers and cannibals? Or how to raise pigs?
Nudity. You're not there. Nobody's there. Result? She is naked and she's studying her body in the mirror. She probably likes to dance around the apartment naked, and she will use the time she spends alone to take off 'all the burden off her'. Like an alien.
Many women wait for their partner to leave so they could put various masks made of eggs, yogurt, oil and similar on their face or hair. She assumes that it wouldn't make a good impact on your libido to see her looking as an extra-terrestrial creature.