Someone who is so good at lying that you believe them even when you know they are probably lying.
Boy: I love you forever, I always have.
Girl: you always say that but then every time I believe you, you disappear.
Boy: I don't what got into me in the past i am so sorry. Honestly you are always on my mind. I promise I am not going anywhere this time.
Girl: you are a Professional Bullshitter how can I believe you.
Boy: because it's true this time and you feel it. I love you I do.
Girl: ya, I love you too.
A few days later Boy acts as though Girl doesn't exist.