Teenagers will be teenagers. I'm one, and I argue and fight with my siblings. But my parents never allow me to run my mouth like that in front of somebody. I may be too old for it, but my grandma would either pop me to stun my jaw, and my dad would spank me. It's embarrassing, so I learned to shut up. XD
I don't think it's so much OOC as it is character development. Nala was extremely rude to Zazu, so why would it differ to a cub she thinks is 'strange'? Also, many kids tone down when they become adults, I'm sure Sarafina learned her lesson about bullying when she was with that rogue pride.