I am not Belarussian so it’s not for me to judge whether this is offensive to the point of banning it but I would say, generally, that the Russian terms for the various ethnicities inhabiting the former Russian empire are best avoided. As the current use of a similar word for Ukrainians (which I’m not even going to type here) shows, things can quickly turn from “friendly banter” to full-on racist, nationalist, supremacist abuse. At the same time, some would argue that such terms were always about supremacy, and I recently find myself agreeing with this more and more.