It depends on the shape and size. Smooth metal spoon in the microwave will be fine, a fork in the microwave will get electrical arcs and possibly destroy your microwave.
Personally I'd just use some kind of metal-free chip clamp instead of actual staples, just to be safe.
It's not even very obvious what won't arc. FreshDirect sells pre-cooked turkey burgers. They come in a metal container with the edges bent over in a way to allow a plastic lid to snap on. Their official cooking instructions stay to just remove the lid and put the container in the microwave. It was surprising, but it doesn't have any arcing issues.
