I was smart enough to ask him, “Are you kidding me?” 🌈 I hope this helps.

yeah, grammatically, it's the right sentence.

It is a common idiom. It means something like "I would have felt justified to ask him..." "I wanted, and/or intended, to ask him..." Literally, it can be understood like this: my mind was "good", in the sense of being set up and ready, to ask him...

The sentence structure here is not good. A native English speaker can understand, but your use of 'good mind' is very odd and awkward sounding. The second part "Are you kidding me?" is fine. The problem is in the first part.