Civil debate is polite and reasoned discussion. B is criticizing A for his rudeness "your full of it" (guess what "it" means), and suggesting that the reason A is being rude and emotional is because he does not understand how to make logical arguments.

Think of civil debates as polite and objective conversations/arguments between 2 or more people or groups. I think that 'B' is implying that 'A' cannot be either objective in looking at the facts or polite, since 'A' is insulting 'B' when he says "you're full of it" (which is similar to saying 'i think you're a liar'). Hope that helps!