1. If it's there first time tanking, healing, or DPSing in a dungeon? Fine. Day 1-3 of new content? Fine. After the third day though, it's a little tiring of hearing the same excuse of "I'm new!"

2. No, this isn't a good excuse. It's not thing to accidentally forget to place something on your hotbar as I've done that beforehand, but it's another to queue up for normal or harder content and then decide that you want to change your UI while you wait. If you're changing your UI in a way that is going to become detrimental towards how you play because you've messed up your finger's muscle memory, then you should iron out the kinks and practice it first outside of content that would require other people's time.

3. Never a good excuse. You don't go to work and lash out at people because you have problems at home, or go home and lash out at people because you had a bad day at work either. If you're sick, you should be resting in bed and not trying to focus on XIV. If you had a bad day, it's fine to vent, but that doesn't mean you get to be an asshole about it either.