“Diamonds may be a girl's best friend, but Nutella and shoes seem to run a close second.”
“Diamonds are a girl's best friend.”
“How about "diamonds are a girl's best friends"? Nope. It should be switched around and pointed out, instead, that your best friends are diamonds.”
“Diamonds are a girl's best friend and dogs are a man's best friend. Now you know which sex has more sense.”
“Forget diamonds or dogs—a girl or boy's best friend is always a high-powered weapon.”
“I used to think that diamonds were a girl's best friend, but now I realize it's carbohydrates. Seriously, I have a French baguette at home sporting a matching friendship bracelet.”