Well, you've probably guessed "nimbus" doesn't mean a cloud here. :) If you guess the meaning from the context, you'll be right in thinking that it means "idiot". My guess is that it's a combination of the words "nimrod" and "doofus", which both mean a foolish person. It looks like something that the writer made up. I had to look up TK - apparently it means "to come", referring to information that will be added later.