The last human (a man) is found in a cryo-pod by some aliens, and an older frog-dude warns them all that humans were incredibly dangerous back when and that it should stay frozen. They do wake him, but I don't recall what happens next. I don't think it proves dangerous. I guess all the other humans had killed themselves in a space-war.
It was from a collection of short stories, but I can't recall its title. I think I read it about 7 years ago.