What ご苦労なこって means here?

Question

I struggle to understand the nuance of ご苦労なこって part in the One Piece panel below.

なこって is short for なことで right?

I checked the English translation, it reads "No thank you." So, can I understand ご苦労なこって as "I appreciate your offer but... (I refuse)."

Answer 1

Yes, こって is a corrupted form of ことで. It's rarely used in reality, and it usually has a scornful overtone in fiction, like in this scene.

This ご苦労なこって may look like an appreciation, but it actually is a sarcasm. It's like "What a (pointless) effort" or "You're working hard for nothing". Zoro is saying Luffy is putting effort to something meaningless.

EDIT: Here are other typical examples of こって:

• のんきなこって。
  Ha, [you] are so easygoing (though you shouldn't be).
• 幸せそうなこって。
  [He] seems so happy (though it's not enviable).

This type of こって is interchangeable with こった (modal-ta).