Sarcasm tends to work much better in face to face conversations (where you have audiovisual cues) compared to a written medium like HN. Considering that a large number of HN members don't have English as their first language, it would either be completely ignored or worse, seen as the opposite of what you are saying.
Your safest bet is to not indulge in saracasm on HN, lest you come across as trying too hard to be "cool".
Its a good idea to first find where your customers hang out. Generally this would be at a handful of forums. The next step is to hang at those forums and mingle with the community. After a while you can approach people directly or start a forum thread talking about your idea and to get feedback on whether people would find it useful.
Your safest bet is to not indulge in saracasm on HN, lest you come across as trying too hard to be "cool".