There's a story about a mid-twentieth century performance of one of the Wagner operas where a swan-shaped chariot is supposed to take the lead male singer away. The swan departed without Leo Slezak, who ad-libbed, "What time does the next swan leave?"
I've forgotten which Phantom got stuck in the angel. The audience was taunting him and he spent about 15 minutes scowling back, trying to remain in character, until the crew figured out how to rescue him.
At a recent production of "My Fair Lady," at Arena stage, in DC, much of the cast had been out the day before with the flu. The actress playing Eliza was visibly ill in the "Wouldn't it be Loverly" scene. She left the stage at the end and the next scene began. Eliza's cue to return is, "Here's Eliza, now," but she didn't show up. Another actor ad libbed, "She must have been delayed." A third said, "Let's sit down and wait for her." At that point, the loudspeaker announced a delay. A few minutes later, the performance was cancelled -- Eliza couldn't go on, and the understudy was still sick.
Twice, I've seen actors break the "4th wall" to tell audience members to be quiet during the performance. Once was at Arena Stage, which is a theater in the round, with the audience very close to the performers. One actor rather rudely told a middle-aged man to stop doing whatever he had been doing because it was distracting. At a matinee performance of "Raisin" in the 1970's (I think), a badly-behaved school group was in attendance. The lead actress gave an impromptu, polite speech about how it was hard to entertain an audience that kept making noise. She got a round of applause from the adults.
You alone can make my song take flight.
