Or....
You could have been courteous and changed seats.
I just don't get why folks here spend more time thinking of witty replies the OP might have used instead of considering that maybe the bulkhead might be best used by a family with an infant.

As you all know: The bulkheads can't be pre-assigned and are the only seats that support a bassinet. Beating the family to the bulkhead request does not mean that EVERYONE in the cabin might not be best served by them having the bulkhead. You know there are others that might benefit from it more than you (elderly, un-accompanied minors, family with infants, those with certain medical conditions) when you request a bulkhead seat.
Yes, they can be preferable seats, but COMMON COURTESY might dictate that you cede them.

That is why we sometime hold doors for people and allow someone less able to enter an elevator first. Common courtesy.

You were entitled to that seat. You are also entitled to storm through the door of a public building and not hold the door for the mom pushing a stroller coming in behind you - but you would lack courtesy if you did so.

As for the FA... maybe there is probably a better way that she could have asked, but she had a point in what she was saying regarding courtesy. Trading for a BE seat is asking too much, but if another acceptable seat in coach was available, it would certainly have been courteous of you to switch.

Consider this when you "score" that bulkhead seat. Being knowledgeable frequent fliers does not excuse us from being courteous to those around us.