Airbnb went from monstrously valued startup to accused unethical spammer in one day. The vacation rental website is taking its investors for a wild ride to the borderline of infamy, just like Facebook, Twitter, Zynga and so many other startups.

Yesterday, TechCrunch reported that Airbnb was closing a $100 million round of funding that valued the company at $1 billion. Investors like Andreessen Horowitz were putting their stamp of approval on the company, which helps people rent out spare rooms or whole apartments to travelers.

But today, another shoe dropped: a competitor presented evidence that Airbnb has been spamming people who list their vacation rentals on Craigslist, including people who specifically indicated they did not want to receive commercial email offers. The competitor, online listings broker Dave Gooden, also showed that the emails were being sent from Gmail addresses in an apparent attempt to disguise that Airbnb was behind them. That's embarrassingly sleazy behavior at best, and a possible violation of federal spamming and fraud laws at worst.

Airbnb's peers have been merciless. The company and its actions were branded "fraudulent," "disturbing," "repellant scumbags" and "unethical," among other things, on Hacker News—a forum run by the very startup incubator that hatched Airbnb in the first place, and a forum frequented by the incubator's other entrepreneurs. It is not lost on these entrepreneurs, or on Airbnb's competitors, that Airbnb could win big with its alleged shady tactics. As one Hacker News commenter put it,

MySpace started out purely through spam...Tim Ferris started out in online supplement sales...People complained about Plaxo doing black hat stuff... they sold ok. People complained about Zynga ripping off other games and about breaking every Facebook platform rule there was... look at Mark Pincus now. People complained about Facebook's Mark Zuckerberg stealing their idea... he does not care.

So it is with Airbnb. Assuming Airbnb's funding deal closes, the company will be getting $10,000 $100,000 in valuation for every single one of the site's 100,000 or so rental listings. We hate to see more evidence that, in the startup game, the short term winners tend to be assholes. Maybe Airbnb will apologize and promise to clean up its act. But there's certainly no indication today to refute the asshole-winner hypotheses.

[Photo of Airbnb founders via Airbnb]