Two and one-half stars. Rated R. 105 minutes By Michael O’Sullivan, The Washington Post Content-wise, there isn’t a whole lot of difference between the crude sexual humor and pervasive vulgarity of the recent “Bad Santa 2” and this week’s “Office Christmas Party.” Both Christmas-themed comedies traffic in the groin-fixated humor, debauchery, slapstick violence, substance abuse and corrosive foul language that have come to characterize much of the modern R-rated comedy world. There is, however, one big difference between these two holiday presents that have turned up under the multiplex Christmas tree, and that’s presentation.