The Cleveland Show - 2009 B-M-O-C- 3-18 is rated/received certificates of:
Big Man On Campus
Basic Medical Officer Course (Canada)
Linsbrothers - 2008 Ben Lins - BMOC 2013 Philanthropy 6-4 was released on: USA: 25 February 2013
Unofficially, BMOC (Big Man On Campus). Officially... there really aren't that many titles that start with B. Some campuses have a Board of (Chancellors, Directors, Trustees, etc.), so "Board Member" is a possibility.
Stradlater is nervous after hitting Holden because he realizes he has physically harmed his roommate and friend, which goes against his usual style of being smooth and charming. He also may be concerned about the repercussions of his actions, such as getting in trouble with the school or with Holden's protective older brother.