'If I could drop dead right now, I'd be the happiest man alive.'
The British value politeness, making faux-pas an ever-present social danger. Whether it's asking someone when they're due when they're not actually pregnant, or commiserating with a colleague on his redundancy when he doesn't even know he's about to be fired, there are faux-pas lurking at every turn.
Faux-pas are inevitable - especially as a visitor trying to understand the complex nuances of British life - but it's how you react to one or recover from committing one that dictates whether it will then become a harmless anecdote or a fiery brand of shame.
If someone puts their foot in it with you, the conventionally British response is to be polite at all costs - a tinkling laugh and a brushing-off the "When is it due?" question, for example. But the offender may well be aware that you are just putting a brave face on their rudeness, which makes them feel worse.
It is perhaps better to make a joke of the faux-pas, answering, "No, I'm just hugely fat." First, it gently mocks them for asking such an absurd and dangerous question, while also implying that you really don't care what they think, thereby letting them off the hook for the faux-pas in the first place.
Likewise, if you are the one making the gaffe, apologising profusely merely invites your audience to give you a spade to help you dig deeper. Never be defensive; as Eleanor Roosevelt scorned, "No-one can humiliate you without your own consent". Self-deprecation will lighten the mood and always makes other people feel better. Admit that you're a tactless oaf, make a joke
Take comfort from the fact that you are not alone and that, handled deftly, this can become an amusing story for both you and your victim.