Someone who has little or no connection with London and but yet constantly tirade about their family member or friend who lives in London. Mentioning it in every sentence as if its the coolest place on earth, and never failing to force a little fragment of the city into a conversation that has nothing to do with London. A common mistake made by people listening to a London Bummer is accidental belief (by the end of the conversation) that the London Bummer has in fact lived in London all their life and has gone from the streets of London, to running its Mayfair complex.
Clive: Sorry I didn't answer the phone, we where shopping in London. Did I tell you my mums got it made here now?
Englebert: Yes you have already bragged about that. Your becoming a right London Bummer.