I would not do it with the dude there, you really can't be 100% sure what the actual plan is, what if this guy gets worked up and get all excited and without knowing he comes up beind your buddy and starts rubbing on his nuts or something? //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif
Even worse what if they are some type of sick tag team raping team and he ends up getting ***** and butt pumped with no lube? Never know but at minimum I would tell him to make sure said BF is smaller than him or at least make sure he is confident he can take him if he has to, especially if this is the first time they have tried something like this never know he could get jealous and flip his script while he is pounding her all of a sudden.