@johnirvine: Think for a moment what your thoughts would be if your departure were delayed due to a passenger arguing with the agent at the gate; as you would have no possibility of knowing what his/her complaint would be and who's at fault, most probably you would side with the agent and you'd certainly not blame the airline for the delay. Is it, thus, worth arguing with the gate agent? Especially in your case when they are not even employees of the airline (and neither is their supervisor for that matter). And I write this fully understanding why you were, justly, angry!