It depends. For picrel, this character hides her nasty side from her friends because she doesn't want to put anyone through what she went through with her emotionally abusive mom, but she always gets her buttons pushed by the asshole of her group, which brings out the worst in her. Ironically, the friend she's the nicest to winds up being closer friends with the asshole because he's more honest with himself.

None of this is shown in the anime, of course.