Slaughter - S = Laughter! Achievement
Slaughter - S = Laughter!20
Use every type of novelty weapon on a zombie.
It is not required to kill them, hitting them will suffice.
As all other multi-playthrough achievements, there have been reports of it not unlocking when it should. Try to contain the requirements in one playthrough, to be on the safe side.
Take note of the following item and ensure you find this while doing the relevant mission
- Funny Painting - "Art Appreciation"
A walkthrough can be found here. A video walkthrough can be found below: