11 people showing up at your house is not so far fetched. If you are liked and the 'friends' feel comfortable around you, it can happen. Just recently, my wife had arranged for a couple we know to visit for lunch. Before they arrived, she got a phone call that the group from field service wanted to drop by. Right... So we end up with a boat load of people in our house for a few hours. And we live out in the country. If you lived in a city with good public transportation (I know, not likely in the US except for a few cities) as is common in Europe, you could easily get a bunch showing up in no time at the same time.
Sometimes, you are the only outlet they have for letting their hair down for a bit.