The first “no” from the FA should have been enough. After that there seemed to be escalation on both sides. The passenger who was denied the Irish Coffee should have just let it go without further comment. I never argue with airline crews or staff, it’s like trying to argue your way out of a ticket with a traffic cop. It’s their airline, their aircraft and they are in charge whether they are right or wrong. I’m not saying the FA covered herself in glory in this case but it all could have been easily avoided.