Bitchmeister is the bitch of
bitches. Meister is the German word for master. Bitch can mean basically anything based on the context. It can be very negative and very positive.
Bitchmeister is also a person calling others
bitches. See e.g. the bitchmeister blog on hans-jschmid.com, a German blog where a guy calls others
bitches and "my bitches".