You shouldn't make fun of people.
John is on a date at a restaurant with his new girlfriend Mary, who is feeling down.
John wants to cheer Mary up.
John gives Mary some heartfelt advice about what he did when he was facing a similar problem.
When John and Mary's waiter is just out of earshot, John imitates his speech impediment in a funny manner.
Mary find John's advice to be very useful, and she is able to put her problem into perspective, which improves her mood.
Mary laughs, the waiter happens to overhear this and thinking that she is making fun of him, he spits in her food.