In Prescott Valley, Arizona, where I live, as in many other places, this takes place in early January, at the local swimming pool.
There is also an Ice Princess contest, men only, in which the winner is determined by the amount of hair on his chest!
Each of the Plungers has to sign in, presumably on a waiver of responsibility for the medical problems that may ensue.
A couple of the loonies brave souls were checking out the water.
So why, you might ask, would any individual leave his warm home on a day when the temperature is hovering in the 40's to jump (however briefly) into an icy cold swimming pool?
Maybe it's the free pancake breakfast with which they are tempted.
And it's not only the youngest citizens of the community who join in.
This fellow claimed to be "only" 58!
He asked me if I was going to join him?
I swiftly declined, thinking to myself . . . "my mama didn't raise any idiot children!"
As a matter of fact, the air temperature was cold enough to send me scampering for home over an hour before the scheduled plunge.
You and I can only assume that they actually did it.