Halloween the third year

It’s been the third time for me to spend Halloween in Manchester. I’m gradually getting used to this custom and finally I was invited Halloween party this year.
Unfortunately I didn’t bring my favourite Ninja costume which I put on at Halloween party in Japan and in America. I needed to find something and went to “One pound shop”. I bought a “Glitter Fashion Poncho” which wasn’t scary but it was matching with my funny sun glasses very well.
One of participants put some boxes in the following photo on his shirt. At first sight I didn’t get the meaning. Do you have any clue?

It’s a serial killer (cereal killer). I like it!