Unless you're building a start up where the potential customers are specifically HN and Reddit readers, get the hell away from those investors. They're idiots.
As lovely and wonderful as the readers of HN and Reddit are, being loved on HN or Reddit means essentially nothing. People here are the magpies of the internet - we love seeing the new shiny thing but that does not tell you it will be a success with the people who might want to buy it. For every Dropbox posted here there are hundreds of Show HN posts that didn't really go anywhere despite having tons of very positive commentary.
If you want to show investors that your start up's product has potential post about it where your customers go and get feedback from people who might give you their money. If you really want to prove your start up has potential, sell to those people and actually get their money. If you can get a sale based on your prototype/proof-of-concept/MVP product that is worth more than a million "Yeah, looks ace, I'd buy that if it was ." posts from us.