Ha! Nice one, Gayle.
It beggars belief..............I say it loads too.
I think Margaret R has got it right with the meaning......to reduce to the status of a beggar, to make belief impossible.
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Old aunts used to come up to me at weddings, poking me in the ribs, cackling and telling me
'You'll be next.' They stopped when I started doing the same to them at funerals.