Why can't you say hi to a drug addict?
They'll say "yea."
Drug Addict Greeting
Explanation
Explain Bear
Listen up, numbskull. The joke plays on the fact that drug addicts often just say "yea" because they're too high to form a coherent sentence. It's funny because it points out the sad state of drug addiction. Bet you didn't catch that, huh? You're probably one of those people who thinks water is spicy.