When someone is said to "need a cheeseburger" it means that the person is way too thin - so much so that the person doesn't look attractive. The implication is that the person is anorexic / dieting too much and needs to put on some weight. Almost always said about a female but a male isn't immune.

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.