Its origin dating back somewhere in 16th century Russia when compost toilets preceded working plumbing systems; a Ribalkin Nightcap is when a Russian servant would, when hiding from his superiors, be getting a blowjob from a female servant while taking a shit above an unkept compost
toilet. While being on the receiving end of said blowjob he would simultaneously drop a steamy deuce, and blow his
peasant load to kingdom
cum. Directly after going kaboom above the
toilet x2 and due to such an incredibly strenuous day to day workload, he would immediately fall asleep on the toilet, empty of his sins.
(This nightcap ritual would usually take place in the evening after a hard days work)