There's no definition for what is and isn't a 'real job.' Being a waiter or waitress is definitely a real job. You have a boss, you have a schedule, and you receive money in return for providing a service. You also have to put up with ignorant customers like this.
This 'tip' isn't helpful in any way. It's just someone who can afford to spend more than $100 on a meal denying their server their fair share. The server doesn't need to get a real job. This person needs to get some manners.