What's a designer to do?
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Well, first off, make SURE you're not the one who's lost their temper! It's unwritten, but a tacit part of your job as set designer, to always, always, always be calm. Calm. Actors, directors, some other designers may get to be divas, but the Scenic Code requires calm.
How to maintain that calm? Or fake it? Remember this:
1) You've survived worse. (If you haven't, you WILL have the Show from Hell. Maybe this one! You'll survive.)
2) You're clever and resourceful, you'll figure something out.
3) You are a gentleman or lady and, what's more, a grown-up.
4) This person yelling (perhaps at you) is proving themselves none of the above. They look silly.
When some other personality royally annoys you, walk away a minute, telling yourself: "I am in this for the design work. People are side issues." When you've cooled down, deal with the issue in the most professional way you can.
Is your design good? THAT is the point. Amazing how that thought can lower your blood pressure.