tell them they're both being A-holes and that you shouldn't have to be the one to sort this out. it's not fair to have you get caught in the crossfire.
My two best friends are fighting for no reason, please help me, they're also pressuring me to choose sides :(; HOW THE HELL DID THIS HAPPEN...?? "HE'S SO ANNOYING AND NOT VERY NICE, RIGHT?!"; "SHE'S NOT A TRUE FRIEND AND A PSYCHO, RIGHT?!"