(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.
White lie
Ken: Yesterday I lost the watch that my girlfriend presented to me. Should I tell her this thing?
Lily: Certainly Not! Your girlfriend will be angry with you. Children and fools tell the truth.