I agree, we somehow feel our authentic selves are either not unique enough or too unique. We conform to some socially prescribed 'style' or way of behavior. I was a poser when I was a teenager, yep. I would often talk a certain way to impress friends, dress a certain way, even sacrifice my own taste in music to listen to what was considered 'cool.' These days I feel pretty somewhat consistent across the board; aside from having to put on a 'professional work face.'
I think a poser is when we try to present ourselves to world differently than who we are, and we're cheating ourselves. Our authentic selves are just as lovable, unique and special as our poser selves. Our poser selves tend to be the boring ones.