This is an acronym from the Peaches Song "Fuck the Pain Away." While "SIS" probably does stand for "Stay In School" "IUD" does NOT stand for "Injustice Under Dog" as stated in the other listing for this pair of acronyms. It stands for "Intra-Uterine Device," a free form of birth control provided by Planned Parenthood. Peaches is encouraging girls to stay in school by not getting pregnant.

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.