I think this is a common nightmare for all of us.
These champions that have no self-insight, wading their way up to the microphone because they think they can sing. 'It sounds great in the shower.'
I normally tell the person to come back towards the end of the night, because as I say, 'when one starts, they all come running'.
They usually accept this, and by the end they have either have left or they've forgot about it. And if they think I was going to call them up, wooops, I forgot. And when you shut down and they approach you with 'why wasn't I called upon' I say :'Sorry I completely forgot.......'

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Roy-Andrè