Silly jokes don't go down well on HN, as they're distractions from the conversation. It's considered "Reddit-like" behaviour, and discouraged through downvotes.
Humour is allowed, and so is downvoting. In practice, the humour has to be to be really good to avoid being mercilessly downvoted. Meta-humour based on usernames and TV shows usually doesn't cut it. Many of us view this as a good thing.
Silly jokes don't go down well on HN, as they're distractions from the conversation. It's considered "Reddit-like" behaviour, and discouraged through downvotes.