Originally Posted by pingu07
i dont understand why diamonds are a girls best friend?
It's just one of generalized phrases. A quite sexist one too. It suggest that girls would value their jewelery, plus the price, and the bragging rights, so much that they'd consider it a genuine friend. Never in a literal context, of course. But it does negatively, and incorrectly, stereotype the great majority of them as being greedy, petty and leaching individuals.
So yeah, it's not a very nice phrase.