'For a start there are friends you don't like. I've got plenty of those. Then there are friends you do like, but never both to see. Then there are the ones you really like a lot, but can't stand their partners. There are those you just have out of habit and can't shake off. Then there's the ones you're friends with not because you like them, but because they're good-looking or popular and it's kind of cool to be their friends. Trophy friends... Then there are sports friends. There are friends of convenience - they're usually work friends. There are pity friends who you stay with because you feel sorry for them. There are acquaintances who are on probation as friends.'
Tim Lott in Mark Vernon, The Meaning of Friendship, p.6.