Dear Cecil:
Is there some specific exercise a concerned citizen can use to get rid of a double chin (his own, that is)? And is it true, as my eighth-grade history teacher used to say, that double chins are caused by sleeping on too many pillows?
— Brian H., Chicago

Dear Brian:
Too many pillows? Cripes, they'll let anybody teach in the public schools these days. Assuming you're not fat or decrepit with age, we may attribute your double chin principally to one thing: chronic slackness in the muscles of the neck and lower jaw. This in turn is usually caused by lousy posture (particularly in the case of people with flat feet), but occasionally by other things as well. For instance, one of Cecil's woman friends, concussively beautiful in all other respects, has a double chin because she had a cumbersome set of braces as a child, which caused her to hold her tongue and lower jaw too loosely--which she still does today.

Anyway, the cure is simple: stand up straight, don't slouch in chairs, jut your jaw slightly both when speaking and at rest, and (if you have flat feet) make a conscious effort to walk on the outside edges of your soles. At the same time, exercise the neck and jaw muscles by standing up straight, pointing your chin at the ceiling, and stretching, rotating your head slowly as you do. Finally, you could probably stand to lay off the Twinkies and lose a few pounds. This job is starting to make me sound like my mother, but I'll do what I gotta do to get the Teeming Millions straightened out.

— Cecil Adams

From: The Straight Dope by Cecil Adams