Queues outside banks - I always thought it was because they were either short staffed or just too many customers. Now I know it's because ATMs are never hole-in-the-walls.
Lavatory seat always left up - I have no idea why. Perhaps to let the devils out? I was always brought up to put it down on pain of death.
No post boxes in the street for posting letters - what's that all about?
Writing your life story on the credit card slip - DNI, signature, name and telephone number (which I never provide)
Saying 'excuse me' when entering someone's house is fine, but saying it every time you go from one room to another seems a bit extreme.
Carrying your keys on an elaborate belt keychain - it used to be very fashionable in the 70s when I lived here and seems confined to the older generation. (as well as keeping your mobile in a leather pouch on your belt)
There are loads more...please add.