Two lifeguards are working together on a beach when one of them notices sharks circling a woman who has drifted out a little too far.  He begins to get up to race to her rescue when the other lifeguard grabs his arm and holds him back. The first lifeguard says,"Why are you holding me back?  We have to go save that woman!"

To which the other replies, "Don't worry.  That woman is my mother-in-law."

"Are you trying to kill her?"

"Although the idea may be tempting, that is not my intent.  Just watch."

With that, the sharks organize themselves beneath the woman, and ride her on their backs all the way to shore, safely depositing her.

"What in the world gave you the notion that would happen," asked the first lifeguard.

"Professional courtesy."