Not a callback - but I cracked up anyway. I was "guest" SM for a musical a couple of weeks ago - long story involving a sick SM and an ASM with no desire to ever call a show... any way... It was Cabaret, I know it well enough, so all good.
Standard pros arch venue, pit with orchestra, 3 monitors on the balcony rail for conductor cam and a kid sitting front row center. Kid figures out that the camera he can see goes to the monitors on the rail. He has a bit of fun making hand shapes and waving at the camera - I can see from my feed on the SM desk and I figure that once the show starts, he will forget about it.
Kid gets bored by half way through act one. Our Hitler Youth takes to center stage, he had been instructed to look straight at the monitor center balcony rail as a focus point. Kid makes bunny ears and hand signs behind the conductor. Hitler Youth chokes back a laugh and tries vainly to continue. Kid starts to pull faces. Hitler Youth chokes back another. Song ends, Hitler Youth power walks off stage and cracks up in the wings. Guest Stage Manager looses it shortly after.