I have recently noticed that if I give my eggs Wedding Cake or Omellette of Regrette the eggs happiness goes down. So if you need that to happen consider eating those. However if you don't want a dark creature I wouldn't give it the omellette because it influences the egg a lot (and it isn't cheap) Also Joyful Cupcake give back happiness so if it's sad and hungry give it that for a double bonus. These are the only ones I know of that do this but I'm sure there are others.