There are six common colloquialisms about cake that I could find, and four of them have origins to do with humiliating African-Americans. It all originates in the nineteenth-century cruel practice of white aristocratic slave-owners to force their chattels and local freedmen to dance around a cake. After all the mockery and laughter subsided, the slave owners would then award that cake to the slave who "danced best". It was a very degrading practice, but since the whites were the literate ones, they got to name the event: a cakewalk, today meaning something very easy. This was because they considered it almost a gift, to bestow a cake for "nothing", and the dancing was an incredibly easy thing to do to earn that gift. This then sprung about other terms, such as piece of cake and easy as cake (both of these became interchangeable with pie in more recent time), meaning "easy" as well, and "taking the cake", describing a foolish action. The other two, non-racist cake expressions I could think of were eat one's cake and have it too (which used to be have one's cake and eat it too, a phrase that makes much more sense) and the cake is a lie, now an official idiom describing a misguided end and originating from the video game Portal. From now on, watch those sugar levels, for they might be racist as well as unhealthy.
Adam Aleksic has been described as the internet's sixth most famous etymologist. He loves writing about himself in the third person, he's a freshman at Harvard University, and he has disturbing interests in linguistics, vexillology, geography, board games, limericks, and law.
The Etymology Nerd