What Am I Riddles

Question: When I come in, someone else leaves, I know everyone, yet no one knows me. I'll meet you all only once in your life, Causing mayhem and mischief and sorrowful strife. What am I?

Question: People pick me, and watch me until they give me power. Then they don't stare in my eyes. What am I?

Question: Unexpected is my arrival. It is announced to all nearby. I protect you, yet you try to supress me. With my friends I embarrass you. What am I?

Question: I get dirty in about 5 days but it takes half an hour to clean me. It takes a long time for me to be tall but I can be short in about 2 seconds what am I ?

Question: You use me. I keep you neat. Every once in a while you empty me out. What am i?