From Homestar Runner Wiki
The Cheatcakes are a specialty food The Cheat originally invented for Strong Bad as a substitute for Grumblecakes, which he had previously been swindled out of by a collaborative effort of Kevin Grumbles and Homestar Runner. Strong Bad did not appreciate the substitute, despite the efforts of The Cheat to add even more steam and sugar than the Grumblecakes.
Strong Bad eventually had a change of heart in the email do over. In retrospect he wished he could have tried one, because they did look "a-pretty good". However, like his other "do-overs", this backfired when Homestar came up with a cheap variation. Homestar, dressed as The Cheat, almost gave him a bag of "Moldy Bread, Guys".
The Cheatcakes have their own "jingle" which encourages people not to eat Grumblecakes. The lyrics are as follows: "Only liars and thieves eat Grumblecakes, and those people go to prison. Just ask The Cheat." This is followed by The Cheat stating, in his language, "Those people go to prison!"