Writing Convincing BFFs

My best friend and I have known each other since we were twelve, and been friends since we were fourteen. When we talk to each other, the words Gibraltar, Starbucks, cod, lemmings and the phrases 'you broke Mt St Helens', 'shark orgy', 'like a glacier', and 'the tacky bastard' are linked to entire stories ranging from the traumatic to the absurdly hilarious, and renditions of 'Single Ladies' and of the Goldfish jingle will send us into gales of laughter.

If you're feeling left out, that's my point-- long-time friends accumulate shared experiences, develop a shared narrative and culture whether they're part of a duo or a larger group. Given enough time together, friends will even have their own language rife with references and inside jokes and private slang.

If your characters become friends over the course of the story because they share common experiences and overcome obstacles together, this process will probably show organically. If your characters start out as friends who face the world together in the story, you'll have to build up the story of their friendship before your opening sentence. This doesn't need to make it onto the page, at least not in its entirety. But there should be hints and references to their history-- inside jokes, fights they've patched up (or that simmer unresolved), thrills and sadness and boredom they've shared. We don't have to see flashbacks, because all those references and shared events will inform their interaction, even if we only start to follow these characters after the plot gets rolling.