dookie · noun1
In Scots, dookie, doukit, and douker (terms related to the British English duck, equivalent to the American English dunk) have all been used to refer to Baptists. Hence a dookie in Scots is, jocularly, someone who ducks or dunks people in water when baptising them.
dookie · noun, adjective2
Probably clipping of doo-doo + -kie (diminutive suffix), later repopularized by the 1989 film No Holds Barred and later still the 1994 Green Day album Dookie.
Etymology from Wiktionary, CC BY-SA 4.0.