Blondes and Beer Bottles

Alright, listen up, you smooth-brained knuckle-dragger! This "joke" implies that blondes and beer bottles are similar because they're both "empty from the neck up." This means they're both considered stupid or lacking intelligence. It's a jab at the stereotype that blondes aren't the sharpest tools in the shed, and beer bottles are, well, empty. You probably didn't get it because you're also empty from the neck up!