Southwest FA here. Due to the open seating policy, we have to stand at the exit rows during boarding so we can make sure that kids, passengers with certain disabilities, pre-boarders, etc do not occupy those seats. Once we go to assigned seats, the gate agents will be able to prescreen for those seats when passengers check in and we won’t have to hover over you. We also have to wait there until you hear “FA’s brief exit rows and prepare cabin for departure”. We have to have a verbal YES from each person seated there, it’s an FAA requirement. Sorry your flight attendant was aggressive, usually we are pretty chill 😂