"You can always tell ambitious women from the shape of our heads. They're flat on top from being patted patronizingly." This is an idiomatic way of saying that women who try to succeed are habitually treated in a patronising manner. People normally pat small children and animals on the head to show affection. The speaker is using this image to suggest how hard it is for women to succeed. People (presumably men in authority) metaphorically pat women on the head, meaning that they treat them in a condescending way and do not take them seriously. The metaphorical 'flat head' represents the experience of having been constantly patronised over a long period of time.

It is a metaphor used by the speaker to describe ambitious women (meaning that they have a lot of drive or motivation). https://twitter.com/tedtalks/status/577993293130235904 I'm a native English speaker and I have never heard it before you posted your question. So it is likely something made up by the speaker to make her point.