I'll be hanged

(well,) I'll be hanged!

An expression of surprise or astonishment, especially regarding some recent revelation. Bob: "You know, if you run your washing machine at night you can save a lot of money on your electric bill." John: "I'll be hanged, I never knew that before!" Well, I'll be hanged! Who knew so many people would show up to see our concert?

I'll be hanged if I (do something)

I am determined not to do something. I'll be hanged if I let some young upstart like you take control of my company!
See also: hanged, if

I'll be hanged

1. I am very surprised, as in, Well, I'll be hanged; there's Susan.
2. I'll be hanged if I. Under no circumstances will I, as in I'll be hanged if I let you do that. Both of these hyperbolic colloquial usages allude to being executed by hanging.
See also: hanged