Lack of Respect
Acting like your friends are worthless when they've been there for you through every disaster.
My friend stuck up for me when I got in a fight, and I called him a nobody. He got a black eye. I got a gold star for being a jerk.
She drove me to school every day and I told her she was useless. I passed the test. She got a ticket.
He gave me his lunch when I forgot mine and I said he was a loser. I ate his sandwich. He ate a napkin.