In the popular video game Minecraft, food (such as cake) can heal your character.
Going "cakeless" is the act of ignoring the cake, and any potential health that it can give you, so you can be a badass instead.
The act of going "cakeless" was developed and popularized by Ray (Brownman) from Achievement Hunter, a popular YouTube Channel.
Person 1: Hey! Why didn't you eat that cake, you would have gained extra health!!
Person 2: Nah, I'm going cakeless