Two couples were playing cards.  John accidentally dropped some
cards on the floor.  When he bent down under the table to pick
them up, he noticed that Bill's wife was not wearing any
underwear!  Shocked by this, John hit his head on the table and
emerged red-faced.

Later, John went to the kitchen to get some refreshments. Bill's
wife followed him and asked,
"Did you see anything that you liked under there?"

John admitted that, well, yes he did. She said
"You can have it, but it will cost you $100."

After a minute or two, John indicates that he is interested. 
She tells him that since Bill works Friday afternoons and John
doesn't, John should come to her house around 2:00 PM on Friday.
Friday came and John went to her house at 2:00 PM.  After paying
her $100 they went to the bedroom, and then John left.

Bill came home about 6:00 pm.  He asked his wife,
"Did John come by this afternoon?"

Reluctantly, she replied,
"Yes, he did stop by for a few minutes."

Next Bill asked,
"Did John give you $100?"

She thinks 'Oh hell, he knows!'  Finally she says,
"Yes, he did give me $100."

"Good,"  Bill says.  "John came by the office this morning and
borrowed $100 from me.  He said that he would stop by our house
on his way home and pay me back."