The term "Bakerloo Line" is used in English slang to denote the activity of anal sex, due to the Bakerloo being coloured brown on the London Underground map. In the same vein as the "Marmite Motorway" and "Bourneville Boulevard" the term offers the ability to snigger like a schooboy for those who know this subversiveness, whilst keeping the gentile innocents unoffended.

Example : "She wanted me to take her up the Bakerloo Line!" (best said in annoying cockney accent)