Friend is a concept. Everything else is a physical object.
eggs are the only thing humanly edible in this list.
silver is the only option you can’t get wet. It’ll tarnish. But eggs get washed. Toothbrushes get wet. Desks get sprayed down with cleaner. And plenty of your friends get wet.
Funny thing about these "odd one out" questions is that the more complex and enigmatical they get, the easier is it to find explanations for each one of them as illustrated by some of the answers here.