my 3 year old does similar things and has for awhile--i know just what you're talking about! with folks/kids she knows she is sweet and kind, with strangers and new kids (esp. her age or younger) she is aggressive and rude. i have interpreted it as her reaction to new situations/new people---essentially her way of being shy or trying to get comfortable with a new person. instead of withdrawing and sticking close to mama as a way to get her bearings, she acts out as a way to get her bearings. it's an attempt to feel power/control in a situation where she feels uncomfortable. i try to acknowledge her feelings, help her identify them, and give her alternatives for how to respond. i often pick her up in my arms and hold her really close and speak quietly to her: "hey sweetie, i know that we don't know that person yet and that might make you feel uncomfortable. it's okay to be uncomfortable. but sticking your tongue out at them (or yelling "NO" or "Bye", etc) makes them uncomfortable too. if you feel uncomfortable, some other things you could do is just stick close to mama or not say anything or i can help you get to know them. if we say hello and smile and make friends, then the situation is gonna feel a lot easier. if we're aggressive to try to show we're powerful, that just makes the situation worse." sometimes then i'll help her go over to the new kid and introduce herself and say hi and talk to our new friend. other times, if the kid has already moved on (like passing someone in a store) she will often times be friendly with the next kid we run into. but not always. i think it is a stage. and maybe a long one. i just do a lot of repetition, take each situation as an opportunity to acknowledge her feelings and try to guide her to a more kind and loving way of interacting with herself and the world. and try to get through to her that being aggressive only gives us a false sense of power. that only by being kind and opening our hearts can we feel true power. being afraid and uncomfortable is okay. projecting those feelings onto others is not. big concepts for a 2 year old! but just being gentle and repetitive helps. good luck!