I believe a "bimbo" IS an airhead. Just that. Someone who pukes rainbows, shits sparkly clouds and lives in their own world where nothing is ever wrong and anything negative is either a "lie" or just "not needed" for the sake of not educating themselves on something.
For example, someone asks for opinions on a drug. They get all bad reviews, because it is a drug that is NEVER used properly and often kills people. So they come back with, "I don't want to hear the bad reviews! Give me something positive!" And then they ignore all the warnings on the bad reviews, turn around, and only reward those who gave positive experiences. Then they skip into the doctors office to get that drug. Because, for some reason or another, they don't think negativity exists, nothing bad will happen, and them dying is so far out of their reality.
I see it a lot in Joe Schmoe dog owner, too. They don't want to hear anything negative, ever, about anything. CM is God, Science Diet is amazing, their dog isn't actually deathly ill, you're just a debbie downer!
It's willful ignorance to be sickeningly "happy" all the time, to the point of calling anyone with anything potentially negative to say a "bully", "debbie downer", "liar", etc. . THAT is a bimbo to me. It has nothing to do with sexual insults, depression, or a positive outlook on life. It's just another class of idiot. Just a happy, realistically blind idiot instead of the typical cocky/pretensions ones we typically deal with in daily life.