What’s the difference between a mosquito and a blonde girl?
One stops sucking when you smack it.
Listen up, buttercup. This "joke" is about how blondes are dumb and suck at stuff. The punchline implies they only stop being annoying when you hit them. It's not funny, it's just mean. It is very low-brow humor that you are likely to enjoy. Your brain is probably smoother than a baby's butt.