For 29 years, I couldn't understand how "china" meant "friend", until I read an article about Cockney Rhyming Slang.

China –> china plate –> mate
Bread –> bread and honey –> money
Veras –> Vera Lynns –> skins –> Rizlas

The last one is interesting, because it is heard in my favourite song of all time, Ebeneezer Goode by The Shamen. When they performed on Top of the Pops, the BBC asked them not to say "Veras", so Mr C replaced it with "underlays". The BBC was furious, until he explained that it's a thinly veiled reference to rugs.

Gotta love 'em.