Buying rounds is out of fashion in the UK, because drinks are getting too expensive and so many people are only buying soft drinks. The days of being in a pub and having the choice of maybe two or three beers all the same price and everyone drinking more or less the same thing is long gone. When you’re in a group of friends and one’s drinking real ale, another has a large glass of wine, another has some fizzy yellow lager and the designated driver is on cokes, buying in rounds makes no sense.
Talking about therapy or money – not offensive, it’s just something we Brits dont consider to be good conversation topics. Nobody ever talks about how much they earn. In some cases people don’t even tell their spouse how much they earn. And you DEFINITELY don’t tell your colleagues.
The main offensive thing is getting someone’s country wrong. Referring to a Scot or a Welshman as English is the height of insult. The “two-finger salute” is also an insult and will most likely earn you a punch in the face.
Describing something as “quite good” usually means it’s a bit less good than just “good”. To be even more confusing, describing something as “not bad” is usually better than “quite good”. But when your wife or girlfriend asks you if you like what she’s wearing the only correct response is “That’s absolutely beautiful, darling”.
On the whole it’s much harder to offend a Brit than it is to offend an American. You can call a Brit a “stupid cunt” and he’ll take it as a light-hearted joke.