That sounds like a huge issue, and if your b/f is seriously thinking that once the dog grows up he'll suddenly be Lassie, he's sadly mistaken and that mistake could seriously cost you in the long run. If not trained from puppyhood to know what is acceptable and what isn't the behavior that he's been allowed to get away with, snapping, chewing, destruction will continue, how is he to know that snapping is bad if no one has corrected the behavior. Bottom line is if you don't take the time to properly exercise him or train him he will continue to be destructive because he's frustrated and bored out of his mind, he will and can cause you and others serious injury if he bites and it really sounds like he's one step away from biting and hurting someone. This dog could be a potential liability of no one is willing to step up and take control of the situation.
If you can't stand up to him about his dog then what about when you have children? Someone needs to speak up for this dog because the dog cannot speak up for himself. He has no quality of life living in a crate no human interaction and no exercise, it's actually considered neglect and illegal. If he's really unruly and bites no humane society will take him, and no one will adopt him knowing he's a handful and a possible biter.
My suggestion is you tell your b/f if he doesn't do something such as training, socialization, exercise etc, then you will take the dog down to the local vet and have him euthanized because that is a lot more preferable than living the way he is.
Dogs don't improve over time, it's called training, exercise, and a lot of hard work.