Interesting topic, Qion. A bit of a thorny one too! I'll try to give you a very honest picture of my experiences.
I think there is a combination of factors. One is that the British sense of humor can be quirky, and so a lot of comments can come across as being aggressive or insulting when they were not originally intended to be. I remember being told years ago that if British people insult you, it means they like you (friends tend to take the mick out of each other), but the worst situation was where they ignored you, which was a sign of indifference! That said, I realize there will be others out there who do mean things in a harsher sense.
There certainly are those who go by stereotypes of fat, sedentary Americans who have little understanding of the world outside their own borders. Then again, the UK has people like that too! There's plenty of unhealthy lifestyles in both countries. I also wouldn't worry about the "Christian" label, I think people are more specifically concerned about Protestant fundamentalism (e.g. teaching Creationism, etc.). While stereotypes do exist, I know plenty of Brits who enjoy travelling to the US or enjoy the company of Americans. It also reminds me of the English attitude towards the French; there's plenty of griping about them, but France is also a favorite holiday destination for many English people!
To be honest, I often find myself in the middle. I've often defended the US to people in the UK, to the point where they thought I was heavily pro-US. At other times, I've encountered very gung-ho people from the US, where I've been pointing out some of the less appreciated aspects of American culture or foreign policy, and then I'm seen as anti-US!
Over the years, there have been some gripes that have built up. When some (not all!) Americans adopt an attitude of boldly wading in and winning World War II for everyone, being the leader of the free world, or having a nation that everyone aspires to, it can get up people's noses. I think some Brits also feel a bit raw, particularly as the British Empire waned after the war, while American power increased, and Britain has only last year finished paying off its war debts to the US (the UK was quite devastated by the War, and the effects were felt for many years to come). More recently, many Europeans I have met feel increasingly uncomfortable about the spread of American culture and American business. While many welcome greater access to these things, there are fears that they must not override existing national characters.
To be honest, if you are noticing a rise in anti-American feeling, I think a lot of it comes from the Bush era. Bush has done America and Americans absolutely no favors abroad. He has done tremendous damage in the eyes of many (I believe the world's largest anti-war rallies was held during his era, etc.). I struggle to think of a time when the US was regarded with more suspicion abroad, and the US has unfortunately become, to many, the bad guy rather than the good guy. The rather simplistic "good versus evil" approach, and the fact that many US citizens are perceived to go along with it, rather strengthened the stereotypes you have alluded to. I remember an astonished debate in the media over here, when the question of "why do they hate us so much" was asked in the US after 2001; the question here was along the lines of how Americans could not know what has been done in their names for decades or, if they did, how they could not expect to be resented for it.
Many Europeans will also feel the world has been made a less safe place by them, due to this foreign policy, and that the policies were not well-founded in the first place. While some Americans refer to cowardly Europeans who won't step up to difficult tasks and who appease regimes, many Europeans will see current US foreign policy as being like a bull in a china shop, leaving a trail of destruction in its wake, and with the expectation that others will pick up the pieces. There is also perceived hypocrisy, when it comes to how America wants foreign nations to behave or comply with their wishes, but won't reciprocate (e.g. "The Hague Invasion Act," as it was referred to...). That doesn't help when it comes to adopting moral high-ground.
Anyway, the above are not necessarily my views, so please don't see it as an attack. I'm just trying to honestly relay what I think could be behind some of what you described. But, hey, perhaps Rhisiart was closer to the point and in far fewer words!
