There are a few things that cause marital strife in my life... When my husband eats my leftovers, driving together and the cupcake vs muffin debate.
  1. My husband says nothing. I say everything. Help save our marriage. You decide.
  2. If there are blueberries in it, it's a fucking muffin
    Suggested by @goobs
  3. If you feel guilty about eating it for breakfast, it is a cupcake
    Suggested by @goobs
  4. Frosting
    Cupcakes have frosting; muffins do not.
    Suggested by @evanp