In actual fact, 'loo' comes from the French l'eau -water, and is an upper-class term. The middle-classes use 'toilet' and the working classes (and schoolboys of all classes) call it the 'bog'. Older people of a certain generation sometimes refer to the 'khasi', hence the Carry On Up The Khyber villain named Randi Lal, the Khasi of Kalabar!