The tens of thousands of people attending Gamescom on any given day were excited enough to be there as it is, but at specially anointed times, they were whipped up into an absolute fervour. And it's quite the sight.
If you need some background, this kind of behaviour (which really kicks in around twenty seconds in during the first video) is a requirement for free t-shirts and other swag. First the MC works everybody up into a lather, then when they're chanting or singing like madmen, said swag is thrown into the crowd for the kids to fight over.
It shakes the convention centre. All in the name of a little marketing. Like I said, it's quite the sight.
As a bonus, the second video is similar, only it's a few hundred Germans going apeshit over Kriss Kross.