As a working class British fella, I'll drink to this!
(Oh god this turned into a rant I'm sorry)
Now I can't speak for the 'Muricans, but in the case of British SJWs who throw around the "FUCK I HATE WHITE MEN!" crap, I think that what's happened is they've absorbed the class-ignoring American SJW stuff through Tumblr and Twitter without then contextualising it and pondering how it might work (or not) under British circumstances, (that is, with regards to British politics and history, both of which have seen social class play a tremendous role) - or if they do, they simply take one look at the middle and upper class men who ran the British Empire and say "SEE, TOLD YOU WHITE MEN WERE PRIVILEGED ASSHOLES!". So all that domestic British history with its attendant "Historical baggage" of the native white working classes being trampled into the ground by their social "betters" (the Enclosure Acts, the Peterloo Massacre, the Tolpuddle Martyrs, the ruthless exploitation in the factories and in the mills - and that's to name only four instances from a long ass list!) gets overlooked. And probably for the best as far as they're concerned; its hard to demonise a white man for having "Historical privilege" when his ancestors were chained to horses and dragged across a field simply for daring to ask for the right to form trades unions, and its hard to claim women have always had it worse when Regency-Era female aristocrats were living lives of unimaginable luxury while the vast majority of the population starved. There's an awful lot of books out there which discuss the idea that white working class British people weren't necessarily or automatically given the "Privilege" associated with their American cousins even well into the 20th Century (Indian soldiers during the First World War tended to be astonished by just how poorly the white working classes lived), but for SJWs that doesn't fit the "Screw white men! They're all privileged oppressive dickheads!" narrative, so it's easier just to focus on people like Cecil Rhodes.
Moreover, a lot of British SJWs tend to be, dare I say, very middle class indeed and focused upon middle class identity politcs, which means that such things as the devastation wreaked upon mostly white, working class men by Thatcherism (which to this day remains a sore spot in many Northern working class communities I'll tell you) don't tend to register in their minds in quite the same way. Therefore, they can throw around the "White male = PRIVILEGED MONSTER!" stuff without realising how quickly that falls apart in a British context; white working class boys (partly because of this legacy of Thatcherism) statistically get the worst grades in British schools, there are entire white working class communities now falling into their third generation of unemployment after being utterly demoralised by pit closures, and the police brutality at the Battle of Orgreave has been largely forgotten in the wake of the scandals around perceived-racist American police violence.
Now that's not to say things like racism and sexism don't exist here in the UK (they do, sadly), but classism against white people is also a huge issue over here which, as I've said, is often overlooked in an age where (partly because of events in the States), the former two are considered to be "More important" - 'Old Left' class politics being overtaken by 'New Left' identity politics if you will.
TLDNR; British kids reading American politics on Tumblr, forgetting they live in Britain where things are different, all white British men are Cecil Rhodes, who's Margret Thatcher, bloody New Lefties.