Generally refers to gay bottom men that are so excited to receive some other guy that they willingly bend over to grab their heels and get into the receiving position. To be more grammatically correct, it should be used as "hands-grabbing-heels".

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.