Actors and actresses are typically informed of nude scenes well in advance, and nudity waivers require directors to state what will be shown and its presentation.
What is normal, expected, or comfortable for them changes with the place or situation.
Until the 1980s, male nudity was rarely shown on screen.
Another example is in many schools, a man must wear a jacket over his shirt, and a woman must wear a dress that has sleeves.
A woman who would not usually show her breasts because of modesty, might be quite happy to show her breast while she is feeding her baby.
They swim nude, lie in the sun nude, but they put clothes or a towel on when they come inside the house.
Sometimes the pool had bathing suits for girls to wear.
When she finds out, it puts a new strain on their marriage.