A crum cake is a delicious desert consumed by a female off a males crum (hence the crum cake). Ideally the male decorates his crum in whip cream and chocolate along with any other interesting treats.
Eric- "Hey Finn, what did you and that girl do after dinner?"
Finn- "She had a scrumptious crum cake, then we drank brass monkeys and she had another crum cake, LOL"
Eric- "Noice Finn, Noice!"