When is it ok to lie?

I dont like people who constently lie lie lie about there life and who they are.but i think small lies are ok,like if Ты didnt want to share your gum and Ты told the person Ты dont have any.but really some lies can hurt others.like telling them there cooking is good,or there outfit is cute,when really your lying to make them feel good.

So when is it ok to you?