Golden Egg level 28 is found in Birdday Party 19-14. You have to destroy the "Cake-TNT", and then the Egg will appear behind the slingshot. Fling the Boomerang Bird backwards to reach it.
Strategy
Fire Terence up, so he should hit the first tower, then the rest of the structure should collapse to the right. Most of the TNT and the floating pigs will explode.