I vaguely remember in the past I heard a father said with a smile, "My stupid boy/son, it is a cat, not a dog." In this context, the father was not scolding his son. It's spoken in a friendly way.
Likewise, I went to grab coffee with my little brother. My order number was 50. My brother said "oh jeez, a cup of coffee is 50 dollars, so expensive!" I chuckled and in a friendly way taught him, "_____, the price is here, $5."
So what will I address him here? stupid/fool brother, dumb/silly boy?
If any of these words are still considered offensive to my brother, when I describe this story to my friends, I guess I'm free to use a slightly offensive words, but still in a friendly way. Would these words sensible?
Some untrustworthy articles mentioned "silly goose" and "goofball". Would they work?