1. The first time Wallace says "Cracking" is when you give him his eggs during the first act.
2. During Act 2 with Wallace, as soon as you can leave the cellar go to the kitchen and flick the egg hammer setting that is next to the door to Tap. Wallace will talk for a moment and will use the word cracking if you listen closely. If it's already set to Tap you may need to flip it to Bash then back to Tap.
3. In Act 3 you must not kill the bees in the front yard,basement, or the one in the bedroom. First you need to clear the bees in the town so then when you go home and go to the kitchen, talk to Wallace, then talk to him again at the blender when he moves over there and he will say "cracking".
WARNING: Wallace will only say this when only the town is cleared, he doesn't appear to say this phrase if you have cleared the bees from the garden or cellar. So make sure you do the town first!
4. In Act 4 when the queen bee gets stuck in the tunnel a cut-scene will occur with Wallace saying "Cracking"
After the final cut-scene the achievement should pop up. Good Luck!