I'm sorry, but sometimes there is a level of incompetence on the stage that's just so insulting to an audience that it's simply not worth enduring beyond one act. It's bad enough that a show has wasted an hour of my time -- I'm not about to allow it to waste two. That said, I tend to stay anyway for most bad shows, out of morbid curiosity, if nothing else. I've seen over 800 (mostly professional) productions and off the top of my head, the only ones I walked out on at intermission were:
The Fantasticks -- absolutely painful. Over the course of those 40 years obviously some casts were better than others -- this one was a real turkey. I left at intermission and half the rest of the audience walked out with me, shaking their heads and muttering to themselves (I even overheard some cursing).
Closer Than Ever -- Found the entire to be experience grating and, I'm sorry, I just hated every one of the songs in the first act. Couldn't wait to leave at intermission.
Hair -- A recent college production I saw was so ineptly sung, acted and directed, that it was an insult to the material.
I'm sure there are a couple of others that I've just completely blocked out altogether.
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
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"The Devil Be Hittin' Me" -- Whitney