(well) I'll be damned! impolite old-fashioned sentence spoken language informal
Well I'll be damned! Our team lost.
I'll be damned if I let you borrow my books!
To be surprised by some sudden occurrence
To greatly surprise, shock, or confuse someone
An exclamation of shock or surprise
This phrase was very popular in the US South. It's not used very much today.
If someone has a cast iron stomach, they have a strong stomach that can digest unusual food and even bad food without being ill.
Jimmy must have a cast-iron stomach, when he drank milk with lime juice and felt perfectly fine afterward.