I've had an actor get very (I mean VERY) upset on a current production because we've put a curtain up to cordon off the men's "dressing room."  I initially thought that their area was sufficiently isolated (a loft full of full garment racks) but found out otherwise.  We are a group that entire families are involved in, thus we had 11- and 12-year-old girls as well as high school student volunteers backstage.  He chewed out my director for 20 minutes (less than an hour before curtain) and when I approached him after the show to ask him if I or someone else had done something personally offensive, he indicated that the curtain was offensive.  "This is 'theatre,'" was his repeated reason. 

Hi actingbee--first of all let me ask what your role is in this production? Are you the producer maybe?
If I'm getting the situation right--you had the dressing room set up a certain way. Then you found out that the men's section wasn't "sufficiently isolated"? How did you find out? Did someone see something they were uncomfortable with and complain?  Was this guy singled out? It's possible this guy could think he was being accused of improper behavior involving 12 year old girls. If he's guilty of that you need to get him out of there right now no matter what. If he's just an actor carelessly changing his clothes in the space he was assigned, then depending on what happened back there and what was said, it could be understandable that he might get very defensive, feel insulted and/or lose his temper.
 Also, yes,  it's possible he's a diva with a bad temper and/or mental health issues. But in my experience, an emotional outburst like that usually doesn't come out of nowhere. Maybe the show's in great shape and this guy's an idiot. On the other hand,  is  there some unresolved ongoing personal or artistic conflict? Have there been confrontations you don't know about? Is the director a screamer? Has she/he lost control of the show? Is it one of those horribly stressful productions where nobody has it together? (Just brainstorming here) Like I said, the show could be in great shape, but maybe the actor was upset about other things and finally lost it over this issue. I'd also bet that with eleven and twelve year old girls and high school volunteers running around in what appears to be tight quarters there's a chance the backstage atmosphere is more chaotic than the norm and might put a sensitive person on edge.
At any rate, I think what needs to happen before the show starts its run is to sit everybody down, show them what's going on backstage, how you do things and what is expected of everyone. The dressing rooms have eccentric people in tight quarters under highly charged circumstances and everyone needs to respect everyone elses' space as much as possible but you know that.
 Assuming the guy's not insane or a sexual deviant, if this is early in your show's run, the courageous move would be to sit everyone down and try to clear the air, smooth feathers, maybe he apologizes, everybody hugs and gets back to doing the show and having a good time.  Otherwise you'll have that cloud hanging over the show ....YMMV

all I can say is Some actors are never happy no matter what you do. I worked with a guy once who would punch the wall before every show... I asked him about it and he said it hurt but helped him focus. You get all types in this busisness

Well, that sounds like the best possible outcome. Sorry to have rattled on about negative possibilities! I'll make a note to myself not to post after having to stay up all night! I'm glad you don't have some unresolved weird situation to deal with.

I'm worried.  If you have youngsters in a situation like this and he dislikes the curtain, I have to wonder . . . "Does your group do FBI background checks on the adults?"