1)A cocky person who thinks he is a senior but he's actually a junior
2)One who wears a North Face jacket without anything underneath and stares at juniors from afar
3)A junior who tries to graduate early

A pick me is a woman that is willing to do anything for male approval. She will embarrass or throw other women under the bus to achieve this goal. The unfortunate thing about a pick me is usually the men they are trying to seek approval from are of poor quality and treat women badly, leaving little real benefit for the pick me.