A Flight Attendant reported a potential escape slide deployment when the caterer opened the door while it was still armed.

Narrative

Prior to parking at the gate the Captain had made an announcement for everyone to remain seated until the seat belt sign was turned off. He explained due to weight and balance on the A321 NEO we needed everyone to remain seated. We arrived at the gate and the seat belt sign was still on when I noticed a caterer in the window at door 2 right. He did not knock but we made eye contact and motioned to him that it was not clear to open the door. We were still armed as the seat belt sign had not been turned off. The caterer then opened the door while the door was still armed. I stood back in shock. I told him we were still armed and his response was 'we don't have to wait anymore for you to give us the ok; we are on a tight turn.' He also mentioned that they could open the door from the outside and it would disarm. I told him the Captain had seat belt sign still on and all the other doors were still armed. He proceeded to change out the galley. I called and informed the Captain then I called the forward cabin to alert them we were disarmed at door 2 right because of the caterers and asked if we should disarm all doors at this point. The seat belt sign then went off and the purser made the announcement to disarm doors; cross check and standby for all call. After the event I was left feeling unsettled and anxious. The caterers action could've gotten others hurt.