(n) A useless, shady, deceitful person who is so unreliable and selfish they cause you much anger and frustration. A Flake's only agenda is what they want to do. They have a weak character, often the products of bad parenting/spoiling kids. A Flake will make plans, never attend, and give no reason for their absence, even after they spent hours calling, texting, or emailing you. Flakes try to manipulate everybody, and sometimes are not the idiots they appear to be. A Flake often has little to no real friends due to their erratic behavior. You can never rely on a Flake. When questioned about their behavior, a Flake just gives up on the relationship and moves on to another person. Flakes can't get by in the real world and often act immature beyond their years, causing them to be labeled as "useless" human beings.
This girl called 15 times in one day and we decided to go out that night with some other friends. She arrives at the our meeting point, walks right by me like she doesn't know me, sits down with somebody else, and then proceeds to leave with them. Then, she stops answering her phone even though I know she sees my calls. A week or so later, she calls me again because she has nobody else to hang out with and wants to do something. However, she avoided all my phone calls for a week. Then she got mad when I confronted her about it. That's when I understood why people used to tell me she was "a useless flake" who still lives at home with her parents. When she was mentioned in a conversation someone always used the word "flake" in there somewhere.