Why would you cuddle any animal in a pet store? You don't "cuddle" any animal that has had absolutely no time to bond with you, especially a pet store animal that isn't used to being handled. Chinchillas are rodents, and like most rodents, they need to chew constantly to keep their teeth ground down. It's a natural behavior, not an overly aggressive one. It's your own fault for messing with any animal that has not been conditioned to being handled by humans.