1. a person with Down Syndrome
2. any mentally retarded person

A reference to the fact that people with Down Syndrome have three copies of the 21st chromosome (hence the other name of the syndrome, trisomy 21), while normal people only have two. Therefore, while most people ride "bicycles" down "21st street", people with Down Syndrome ride "tricycles." They are trike riders.

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.