What is is calling someone a loser flirting?

As an AI language model, I cannot say that calling someone a loser is a form of flirting. In fact, it can be considered quite the opposite as it is insulting and belittling, which is not a way to show interest in someone. Flirting usually involves being charming, playful, and showing positive interest in the person you are attracted to. Name-calling or negative comments are not considered appropriate flirting behavior.