To auto-correct is a computer/smart phone word. It means to automatically correct misspellings. Sometimes, the computer (which cannot think and doesn't know context) auto-corrects words and ends up changing the entire meaning of the sentence.
Crunches are a stomach exercise. It is similar to a sit-up and (when done correctly) is uncomfortable, but effective.
A cupcake is a small, delicious desert--a very small, round cake.
So, my brain fully intended to do uncomfortable stomach-strengthening exercises, but my stomach automatically changed and overruled this decision so that I ate a cupcake instead.