FA said I could get banned for using the front bathroom in Premium

On my flight today I was in row 6 Premium. After two hours with the seatbelt sign on, I really couldn’t wait anymore. The line in the back was crazy, so I walked up front. The FA blocked me, I explained quietly, but she still flipped out and even said I could get banned. I went anyway, apologized coming out, but she was steaming. FC passengers were staring in pity. Felt super unreasonable.