Piece of Cake

When teacher asked what exasperation meant, I thought that was so easy, a piece of cake, but that was a presumptuous mistake; I'm still unconvinced and quite dissatisfied after looking it up in thick dictionaries for the sense it's supposed to make; I found out lately it's simply how you'd feel when you want to swat a fly in exchange for something too difficult to take; the sly fly won't budge for it's happily perched upon a red, luscious cherry right there at the center of your birthday cake !