A vagina that is on the rag (having it's period). It may even have bloody chunks due to it being the worst time of the month. The pussy in question might otherwise be tasty and / or attractive - but not really very much so at this particular moment.
Actually eating (going down on) a 'Crimson Custard Bucket' would most likely result in acquiring Red Wings
Guy to GF: Honey can we do the wild thing?
GF to Guy: I'd love to - but only if you're willing to plunge into the Crimson Custard Bucket .