Green’s Dictionary of Slang

mercy buckets phr.

thank you.

1960		‘Nino Culotta’ Cop This Lot 80: ‘Merci, messieurs,’ he said. Dennis said, ‘Mercy buckup ter you too, mate.’.
1979		G. Swarthout Skeletons 240: Oh my God Annie. Mercy buckets!
1983		New Society 10 Mar. 384/2: Meals begin with ‘horses doovers’, are accompanied by ‘dray wait wane’ or ‘bow-jollies.’ ‘Thank you’ is ‘mercy buckets’.
1996		Eble Sl. and Sociability 79: Merci beaucoup ‘thank you very much’ [inspires] mercy buckets and mercy buttercups.