There's the possibility that he is spoiled in the sense that he doesn't need to follow rules. In some dogs this lack of rules results in them compulsively eating anything they can chew, even if the items are not edible.
Your dog knows exactly that he isn't allowed to take things from the table. He does so anyway because he learned that there will be no (immediate) consequences for him when he takes things while no-one is there. For negative reinforcement to work, you must reprimand him within 3 seconds of him misbehaving.
If you don't have rules in your house he has to follow every day, he is not used to following rules even if no-one is watching him. Since he's male, his general tendency to dominance makes him ignore rules that are not enforced strictly.
Some very good rules are:
- The human always walks first through every door. He is not allowed to squeeze through.
- When humans eat, he must wait at a respectful distance. That means lying at least 2 meters away from the table. The best way to enforce this rule is to place pillows, blankets or bath mats in a spot and sending your dogs to wait on them.
- He never gets food directly from the table or while humans are still eating.
- He is not allowed claim a high resting place like on a sofa or bed. If you want to allow him on a sofa, he can only jump up after being invited by you. If he jumps up without your invitation, send him down again immediately.
These are very simple rules that enforce your own dominance without ever punishing or hurting your dog. You must treat both dogs absolutely equally and enforce the same rules for both. When you start enforcing your own dominance this way, you should notice a change in his behavior within a few days.
Another possibility is that your dog is actually bored and takes the things just for fun. This also has the potential to develop into a compulsive eating disorder called "Pica". You could play different games with him to entertain him more:
- Scent games: (this works like thimblerig) let your dog sit down and wait. Place 3 - 5 dessert bowls upside down on the ground. Put some treats under one bowl, but pretend to put treats under all of them. Your dog has to sniff out the bowl with the treats.
- Search games: send your dog into one room and let him wait there. In a different room where he cannot see you, hide 1 - 3 treats in different places he can (and is allowed to) access. Call your dog and let him search for the treats.
- Balance games: teach him to balance a treat on his nose or head and only eat it when you give the command. This is a great way for him to gain control over his impulses.
- Object recognition: teach him what a "ball" is and what a "plushy" is. Send him to retrieve the object you name. (Please take into account that dogs cannot recognize speach as well as humans, so choose names that are clearly different from each other. "Flower" and "power" are too similar for a dog to recognize the difference.)
- Offer him a toy like a Kong or a kibble dispensing ball.