My personal favourite is '4LAV' a Four Car Lavatory Unit (Lavatory in one car) - that's the description. Anyone seen one?!
Know them well from my time at Essex House Croydon (Central Divsion
HQ▸ Now demolished!).
Used to work the Brighton semi fasts. Coming down from Claydon tunnel the seat went one way the racks went another and the slam doors rattled in sympathy. I believe they known as "Thunderjugs" or something similar.
Like all Southern units they were built to last and did over 30 years up and down the Brighton line, how many million miles they did I don't know.