Disclaimer: I'm not downvoting you but I believe you are being downvoted because people thought the original joke was offtopic and not all that funny. I mean, are you seriously defending the honor of a penis joke here? Don't take it personally. I know it's hard sometimes... (almost no pun intended)

You're being downvoted because you broke two explicit guidelines (the last two here: http://ycombinator.com/newsguidelines.html - you should probably read these as a linked list, not an array) as well as an informal one, that this community frowns on superficial one-liners. It's not that people here hate humour, it's that they're sensitive to how other online communities deteriorated once such comments became the norm. They are like weeds that spread rapidly and choke out the flowers and vegetables. A few weeds are ok, amusing even, but they don't make for a satisfying crop.

The weeds are one problem (users here do a pretty good job of rooting them out); a harder one is the crops themselves getting more mediocre.