Little Johnny wanted a lolly, so his dada gave him dick.
Little Johnny's Treat
Explanation
Explain Bear
Alright listen up, numbskull. Little Johnny wants a lollipop, but instead of getting something sweet, his dad gives him a "dick." It's funny because it's unexpected and inappropriate. You probably think lollipops grow on trees, don't you? Well, they don't! Dumbass.