Refers to any fun activities which are enjoyed only by members of a clique, the fact of which is often purposefully made obvious to anyone existing outside of said clique in order to make them feel inadequate and left-out. Refers to "Rudolph The Red-Nosed Reindeer".
Joey and his small group of friends at school would never let Michael play D&D with them. Michael later realized that they were just a bunch of elitist faggots taking pride in their reindeer games.
Any group team-building activity used by middle-managers in corporate America to pacify and relieve tension among their underlings. Reindeer games typically involve taking a beloved childhood game and butchering it by making the activity company specific. Ironically, reindeer games rarely have the desired effect, as the employees are most often annoyed or, in some cases enraged, by their forced participation.
Bill: So Phil, did you finish that project yet?
Phil: No, I had to go down to corporate HQ yesterday for some fucking reindeer games. God, my boss is a stupid cunt.