If Mumsnet is anything to go by, I'd feel well within my rights to observe that the British are class obsessed snobs, dismissive and ridiculing of anything that's seen as an American influence. Yeah! Cos that's not at all dismissive, ridiculing etc. Juding the UK by Mun=msnet is proably only 1 step away from judging us by Jeremy Kyle... no, wait... 
Baby showers, "gender" reveals, naming conventions (ewww, Madison is just soooo American sounding"), Halloween, Santa To be fair they are Americanisms that either have age old UK versions tha thave been usurped by American tv or are just excuses for a party, again suggested by the vast amount of American tv we get.
Madison, for example, is a bike race or an English surname that is popular in the US because of place names etc. And it is a female version of Matthew, apparently!
Again, it is just different social mores that become jarring out of context, the more so due to a common language and expectations of similarity!
I can see why it is so irritating. It's not like we don't have a shitload of history over here in the first place!