An interesting insult! It i means that you are a douche bag, or a jerk. Its usually used by friends to throw another off his game. They focus in on the word used and forget what they are even talking about.
A more literal term of course is a waffle filled with male ejaculation.
"Dude your a fucking cumwaffle." (Reaction) "Wtf? did you just call me a cum waffle?"
A person who is being irritating or stupid. Cum waffles are the definition of the person who wants to leave the party early and never answers your texts.
Last night Kristen was being such a cumwaffle I wanted to punch her in the face