A good boss should be liked, feared and respected by his or her employees. That last one is essential for an efficiently run business, and employees will always work harder for a boss they like. In no way is it helpful if servers want to stab their boss with a fork.
People in the restaurant industry might need a thicker skin than people in most other professions, because almost everything said in the heat of a rush is an exaggeration of someone's actual feelings. Still, no server should be told to kill himself.
I worked for an owner who told multiple employees that they should end their lives, and I can't imagine any of them worked harder for him after that. He seemed to have a special penchant for berating younger, female servers to the point at which they cried. It was like their tears gave him energy. He suggested one waitress tell her parents that they'd failed because they raised a girl who became such a terrible server.
This guy tended to hit the bottle a little. In this case, "little" is defined as two bottles of wine over afternoon paperwork and champagne or vodka for the rest of the night. If he needed to drink that much to get through the work day, then a profession change was in order.
The restaurant business is all too cluttered with owners and managers like this -- old, bitter, jaded bosses who spew a disproportionate amount of venom at their employees for small mistakes. I get it that twenty or thirty years of telling a revolving door of servers that the silverware should be placed a thumbnail-length from the edge of the table will make anyone a little insane. But that's what they signed up for. If restaurant bosses can't repeatedly correct their employees' mistakes without attacking their character, then they lack character themselves.
I'm not saying a boss can't make use of a certain amount of fear: Employees should be afraid to screw up around their boss. But there's a healthy balance between fear of letting a boss down and fear that affects your s ability to do your job.
Owners and managers: pick your battles. I know you're pissed that a waiter just dropped a couple of plates, but no one drops plates on purpose. As fun as it is to make a loud crashing sound that alerts the whole restaurant to an embarrassing failure, it's just not high on most servers' to-do lists. Screaming "I can't believe what a fucking idiot you are!" will only make that server nervous when carrying plates in the future.
Save the most cutting insults for employees who are lazy, unprepared or purposefully doing a shitty job. Or if the employee is that bad, fire him -- don't keep him around to be a punching bag.
Besides, how many self-respecting employees are going to listen when their boss tells them to see a doctor to make sure they weren't given a mouse's brain at birth and think: "He's right, I'm going to have that checked. Then I'm resolving to do better for my boss because he was honest and is looking out for my health...."