There's a really great book called Odd Girl Out that explores how, because girls lack cultural permission to directly express anger/competitiveness within friendships, they are socialized to express these feelings through indirect/relational aggression (aka the 'passive-aggressive' type of behavior you're referring to, and the type of bullying people are claiming occured in T-ara).
I agree that that behavior is more common among girls than guys, but my problem with EYK's statement is that they say girls are just generally catty rather than considering the factors that cause girls to typically express anger differently than guys. It's caused by social expectations on women, not an inherent female quality.