Unicorns.
Their owners don't pick up their droppings.
In the tech world, unicorns are startups valued at $1 billion or more, and they numbered 145 in November 2015, totaling around $500 Billion in paper wealth. Investopia noted, "they can't all be the next Google."

What is amazing about this current tech bubble of unicorns is how it's being sold to us - the same way the last one was sold.

Each day there's a new report casting gloom on Silicon Valley's herd of magical billion-dollar "unicorn" start-ups: missed targets at Zenefits, share markdowns at Snapchat, a cash crunch at Jet, an executive exodus at Rent the Runway. Dropbox faces doubts about its revenue potential. Theranos is losing business deals. And don't forget WeWork's highly risky real estate deals, and unrealized revenue projections at Lyft. Flipboard failed to find a buyer. Square priced its IPO underwater. Zirtual and Homejoy — not unicorns, but highly valued and highly funded all the same — abruptly shut down.
Each new report is shocking because we receive little information on the health of these private companies — we know only what they choose to share. Usually those are impressive-sounding figures like "400% revenue growth" (from what base? $1?) or a robust "revenue run rate," a decidedly non-GAAP measurement. Worse are the totally meaningless, hard-to-contextualize stats: Start-up X has reached 5 billion "impressions" per month! (But what about profits? Does this revolutionary business model actually work? No comment.)

It's almost as if people have forgotten that run-rates and impressions and "decidedly non-GAAP measurements" were used back in the 90's.
Even the FANG stocks (Facebook, Amazon, Netflix, and Google) aren't impressive.

"Amazon and Netflix aren't even growing that great. On a relative valuation basis you can find stocks growing three, four, five times more than the rate of Netflix," Udall said. "Google is only growing 2 percent year-over-year; It's not inspiring."
"I can find 50 companies growing far better than them," he added. "Maybe they're not quite as big as Google, but they're large-cap stocks. And Google is the cheapest of those four stocks."

Startup Delivery Hero is valued at $3.1 billion.

"Hasn't pizza delivery been around for years?" Wrabetz wondered.

Uber will revolutionize the entire global transportation system. Airbnb is permanently changing the way people get temporary housing.
Right. Put me down for a wooden nickle.

Facebook purchased Instagram for $1 Billion. A company with 13 employees and zero revenue.

It's all delusional. Consider this example.

Just consider two firms that operate in cloud storage: Box and Dropbox. Dropbox is private; Box is listed on the New York Stock Exchange. For no obvious reason, Dropbox garners a significant premium compared to its public peer. T. Rowe Price and BlackRock invested in Dropbox at a $10 billion valuation. But if it traded at the same revenue multiple as Box, the company would be worth $3 billion. What’s the difference? When reality isn’t sexy, investors throw money at potential.

Of course the bubble can be measured in more ways than just stock valuations. Remember how in 2004-2006 everyone wanted to be a real estate agents because of the big paychecks?

consider the over-the-top confidence of Silicon Valley employees. They’re commanding ever increasing wages, with reports of $500,000 annual pay packages offered to recent college graduates. Interns are making $7,000 or more a month.

There are signs in recent months that the tech bubble is losing air. If Dot-Com history is any guide, the bubble will take a year or two to deflate. So while declaring a bubble is controversial now, it'll be "obvious to everyone" at this time next year.