Can be used in two different ways. One way being shock or surprise. The other way is more of a stubborn, selfpride thing meaning you refuse to do something, say something, believe something, etc.
Well, I'll be damned. Kenny fell in love with a hoe.

Or

I'll be damned if I stress over some girl.
by CTFMNiyah September 11, 2013
The veteran Confederates watch as the new VMI cadets hold their formation in the midst of murderous Yankee canon fire
Veteran 1: I'll be damned.
Veteran 2: If I didn't see it with my own eyes...
by DarthKieduss June 5, 2017
To express surprise or shock. Mostly used in the southern United States.
Guy 1: Come here dude. You gotta look at these tits. They're huge.
Guy 2: Well I'll be damned!
by Evil_Jesus February 27, 2009