My favorite pun i made is when SnapChat glasses came out. I stated: "OH - great! birth control for your face! I hated condoms anyway." It started blowing up. Tons of points. It was going to be stuck as the first comment the entire day. Someone (dang) made it go to the very bottom - which is fine - this isn't reddit.
I think the bar for upvote receiving humor is just high on HN
Being funny is fine, but comments that are just jokes and don't actually try to contribute to the conversation are seen as off topic and often downvoted.