Yggdrasil = Yggy (no multibit designation needed, hence no "mby")
Gungnir MultiBit = GuMB = Gumby
Bifrost MultiBit = BiMB = Bimby
Modi MultiBit = MoMB = Mimby? (although you could argue that its taking the i from the end of Modi, so MiMB)
Amps
Jotunheim = Jot
Ragnarok = Rag (I've read Raggy as well, I think that is to align it with Yggy)
Seems like those are the main nicknames for Schiit gear that I've seen used most often.
I'm all for the nicknames in that it adds a sense of ownership like mentioned a few posts ago. Of course everyone is entitled to their own opinions and how they want to refer to things. If you don't like it, don't use it, but don't condemn those that do use them.