I'M (OR I'LL BE) DAMNED IF
Meaning of I'M (OR I'LL BE) DAMNED IF in English
I'm ( or I'll be) damned if
informal
used to express a strong negative: I'm damned if I know.
→ damn
Concise Oxford English vocab.
Сжатый оксфордский словарь английского языка.
2004