I once put an ugly big fake bug in the washroom at a retreat. The first one in screamed, then the braver ones discovered it was fake. I never told it was me. At that time I bought it in the toy section , I don't know if you can find them now.
It's fun to put fake ants around at a picnic too. If you can slip one onto someone's plate while they aren't looking it brings an interesting response. Life should be fun!