"Sun Tan" joke

A rather well-proportioned secretary, Joan, spent almost all of her vacation
sunbathing on the roof of her hotel. She wore a bathing suit the first day
but, on the second, she decided that no one could see her way up there, and
she slipped out of it for an overall tan. She'd hardly begun when she heard
someone running up the stairs; she was lying on her stomach, so she just
pulled a towel over her rear.

"Excuse me, miss," said the flustered little assistant manager of the hotel,
out of breath from running up the stairs. "The Hilton doesn't mind you
sunbathing on the roof but we would very much appreciate you wearing a
bathing suit as you did yesterday."
"What difference does it make," Joan asked rather calmly. "No one can see me
up here, and besides, I'm covered with a towel."

"Not exactly," said the embarrassed little man. "You're lying on the dining
room skylight."