The food stands out. Like Australia has too many fat people too, but our restaurants don't cater to them like America's - don't try to feed everyone a meal suited to a 200kg man trying for 300.
Agreed to both of these points, though as an American I will say there are healthier options, it's just that they make those cost twice as much as the cheaper, unhealthy options.
Most of the food comes from fast food along stroads. It is a core part of the problem. The education system is probably the root, but I wouldn't expect a tourist to understand that.
Snigger is just a variant form more common in the UK, where snicker is the preferred one in the US. Though I wouldn't put it past a 4chan user, it's also a perfectly normal word they may have learned being taught and exposed to UK variants of English.
I thought, and a quick Google confirms, that it is used in the Harry Potter series a few times. Obviously, you might not have read them, but for people in my cohort, that was likely our largest exposure point to British culture.