Looking up stern this morning. Found this:
the rearmost part of a ship or boat : he stood at the stern of the yacht.
• humorous a person’s bottom : my stern can’t take too much sun.
I’m still getting some writing done, so I won’t take a half-hour to come up with some ideas for what utterance could have prompted this latter one (“They’re holding tryouts for the Coppertone girl” is the first thing that comes to mind), but here you are. From my Mac’s New Oxford American.