The underlying cause is fairly mundane - economy.

Recession, rising prices, poor job and life prospects, low income and income opportunities, sub-par civil liberties. There was no "that one thing" and it wasn't about overthrowing the government - all governments screw their people in one way or another, everywhere.

These classify as causes. Unrest however needs a spark and this is what happened here.

If people want change, they need power. And in a country, government has power. So by consequence, to illicit change, change government. In a democratic regime this would mean elections. Lacking that option ...

Food prices are also increasing everywhere that is not first world for a bunch of factors. The US largely immune due to how fake the food is and utterly massive farming subsidies. Of course it doesn't help that most of the world spends a whole lot more than 10% of their income on food(compared to the US).

Yeah, like you guys said, there is no one reason, it's just a lot of bad stuff that finally snapped.

I'll add to the given reasons the fact that the last government was comprised mostly of money-hungry businessmen who came to power by exposed fraud elections under Mubarak's nose and abused their newly acquired power to dominate the financial world in Egypt, like this guy who used his political position to run a monopoly on the egyptian steel market. People here harbor deep hatred towards these businessmen. They are considered by egyptians to be one of the main causes of economical troubles that downgraded the whole society in the recent years.

Btw, I'm not egyptian, I only study here.