Looking for an advice regarding my recent incident with GA a MIA. Was boarding with group 2 (BP group 1) and was stopped by the agent who said that I cannot board with 2 bags (backpack and carry on) b/c I'm in exit row. I called her out on this as to the best of my knowledge this is not a rule. Then she said that this is because my backpack is too big so I offered to be reseated to non-exit row to which she said that she cannot do this b/c the flight is full and that I must check my carry on. I offered to measure my backpack to prove that it's not too big (I've been flying with it for over 2 years now and had only two issues similar to the one today -- one in MIA and one in CLT [in all fairness the for the CLT flight I stuffed it to the brims so it looked huge]) but she refused. Then I asked to be able to take a photo of her name tag but she refused and said she'll write her name on the paper. Once I asked for the name tag she basically threatened/informed (felt very passive aggressive so not sure to what extent it could be interpreted as a threat -- I certainly felt this way) me that she will report me to AA corporate so that I have a permanent record that I'm flying with too large bags for future travel. I obviously then just shut up left my carry on and proceeded to board. Lo and behold guy in 17D (I'm 17F) has both backpack (under the seat) and carry on in the overhead. I actually took a photo of my backpack totally fitting under the seat in the same manner as the one of the 17D passenger.

I wrote a complaint to AA reporting the whole incident and asking for (1) clarification on whether I can have two items (carry on + backpack) in exit row; (2) whether I have a permanent record with AA regarding my backpack and whether it means I cannot fly with it (I offered my photographic counterevidence but there was no place to attached a photo) and (3) asked for additional training for the agent should I (rather than she) be right.

So question to people here. Is this basically a MIA thing? I try to avoid this airport as much as I can (e.g., Admirals at D30 today was insanely overcapacity) but it's hard to get to Carribean another way. Is permanent record for a too large backpack a thing? And do I have to stop flying with this backpack? Basically are they going to be pulling me aside now every time I board? The agent did seem threatening to me and I fly a lot so I don't want to be in this situation. Is there any way to defend myself against GAs accusations? I have photo evidence. Thanks!