This was told by one of the really fun couples I met:  All I will reveal is the the husband often has to get up very early to do irrigation on his crops.  When he returns, he often finishes the night on the couch to avoid waking his wife, and sleeps a little later to compensate.  The wife, on the other hand, happens to be a very early riser – a morning person.
After one such round of irrigation duties, the husband is asleep on the couch around 4:30 or 5 am.  He awakes to the knowledge that his undershorts are slowly being pulled off.  Here’s the exchange:

Husband (groggy and puzzled):  Honey??

Wife:  Sshhh!  I’m laundering whites!