Being able to complain to my MP over coffee. Knowing several people with K's and O's and so on socially.

Walking into a building older than the United States on business. Actually putting to use a building that's been in continuous use by the same organisation since the early Middle Ages. Sleeping in a building people have postcards of, and not because it's a famous example of some kind of modern architecture.

Knowing how to open champagne quietly, and not because of having worked behind a bar. Being able to open vintage port without getting sediment in it. Knowing that you pass the porter to the lift.

Knowing my wines, cheeses and dogs. Knowing my horses would also make me feel posh if I actually knew anything about horses, which I do not.

Doing a pretty good impersonation of the Duke of Cambridge without changing my native accent.

Being able to wear white tie and tails without using anything clip-on or pre-done. Knowing the way you actually signal that you tie your own bow ties, and the very easy way to fake that that all the public schoolboys will actually do, because tying your own is a faff.

Owning my own tailored dinner suit. Having an old school tie and an old College tie. Knowing that a certain stripe of old boy will misinterpret the word College and frown at the obviously wrong tie until I clarify.

Speaking Latin as someone who hasn't studied ancient Rome academically.

Owning a cravat with a pattern specific to my own ancestors, and being able to name those ancestors back to around 1500 (part of this is cheating because there was an old family first name for 200 years). Being able to humblebrag that the pattern is ghastly and the family provenance really depends on how much a certain mediaeval Scotsman is to be trusted.

Being pretty sure that if I gave my surname you'd be familiar with it.

Seeing a relative depicted in a famous historical drama (though not my direct ancestor).

Having had Chatham House Rules chats with people you may have seen on TV.