"I went into a clothing store, and the lady asked me what size I was. I said, 'Actual'. I'm not to scale"

This quote by Demetri Martin is an amusing way of expressing the concept that all of us have an idealized version of ourselves that we make every effort to attain. The speaker is implying that when the woman asked him what size he was, he was referring to his idealized variation of himself, which is not in fact achievable. He is suggesting that he is not able to reach the level of excellence that he desires, which he is not "to scale" with his idealized version of himself. This quote is a funny way of revealing the idea that all of us have an idealized version of ourselves that we aim to accomplish, but that it is frequently difficult to reach that level of excellence. It is a pointer that we ought to be content with who we are and not pursue an unattainable level of perfection.