Blonde jokes are generally based on baseless stereotypes of blonde women. For example “Why do blondes use panties? To keep their ankles warm.”
My favorite blonde joke (and there are lots of variations online) goes like this.
A blind guy goes into a bar and asks the bartender if he wants to hear a blonde joke.
The bartender says “Before you tell that joke, you ought to know that the guy sitting next to you is a wrestler who weighs 200 pounds and is blonde. The guy on the other side is a boxer and weighs 250 pounds. He’s blonde too. The guy next to him weighs 300 pounds and is a football player. He’s blonde and I am too. Are you sure you still want to tell that joke?”
The blind guy says “Nah, now that I’d have to explain it four times.”