Board Thread:Questions and Answers/@comment-93.36.207.144-20130923115606/@comment-73.72.92.111-20160624000112

BM stands for brown man. Ray wanted geoff to add it into the gamertag when they were changing it without Ryan's permission. Ray joked that Ryan is such a big fan of Brown Man (Ray himself). You can see the proof in their shenanigans video episode 1 when they filmed them changing the gamertag: https://www.youtube.com/watch?v=euwwOobEgRE.