Stereotypes are dumb but what's even dumber are the people that believe them. No one should generalize a whole group of people expecially because they haven't met them all. The us is a big place filled with many people from all around the world, we come in all different shapes, colours, and sizes. : D
I'm an Aussie and I just traveled the USA.
The general stereotype for Americans is far from what actually is. I found Americans were generally good people. There were some ******** that tried to rip us off but you get that everywhere you travel.
I do believe that the majority of people who believe Americans to be fat, lazy and stupid are those who have never actually been to the States and who watch a lot of American Pie and Jersey Shore.
As for lazy in particular, I just spent half a year living in South America, and the nation I was in had at least twice the holidays that we get at home in the US. They only had classes four days a week, too. Lazy Americans? Not North Americans, that's for sure.