An act, quote, or action that is thought to be badass and a daring or funny move that was extemporaneously thought of and is above what other people are willing to do. Such a thing will bost your rep (reputation) and keep it high, so high that you will become a cool and known member of society. A rep booster does not have to be an act or action, it can just be something that you dare someone to do or something that you are recalling you have done, then the remark "that's such a rep booster" is often used. A rep booster that is in question may be brought to the house of reps.
Steven: Doing something raunchy and completely against society is such a rep booster.