I have some pans with deep gouges in them from "someone" getting exuberant while cutting a cake. And I am quite sure that the "someone" was not me. :(

I know that plastic knives are very sharp, as a friend of mine husband was cutting some meat at a picnic and slipped and sliced his hand. He needed 10 stitches. Wow.

Regarding plastic utensils in general, I do keep them around for things that only need a little something and rather than wash lots of spoons, forks and knives, I just use them.

I use the plastic knife sold as a lettuce knife. I have a large and small one and they are pretty sharp as the edge is very thin. But will not scratch metal.