In the movie As Good as It Gets Jack Nicholson's character, Melvin Udall, suffers from Obsessive Compulsive Disorder. Obsessive Compulsive Disorder, known as OCD for short, is a type of anxiety disorder.
In this movie, Melvin displayed many compulsions. When he comes back to his apartment he locks his door 5 times and turns on and off the lights 5 times. He also washes his hands with 2 new bars of soap each time he washes his hands. When he walks, he avoids stepping on any cracks. He also sometimes repeats words quietly after someone has said something. Instead of trusting one, his has two clocks side by side near his bed for an alarm. These are just a few examples of the many compulsions Melvin has. He always displays rituals such as tapping his toes all around his slippers before putting them on.
One of Melvin's main obsessions is with cleanliness and sanitation. He was a complete germaphobe. Besides how he washes his hands with brand new bars of soap, he also takes extremely long showers. When he goes to a restaurant, he brings his own set of plastic ware instead of using the silverware provided at the restaurant. He even puts on plastic gloves before picking up a dog. Another obsession he has is not being touched by other people. In fact, he doesn't like being around other people much at all in the beginning of the movie. One person that he is really fond of is Carol, the waitress that waits on him everyday when he goes to the same restaurant and sits at the same table. He always orders the same thing and throws a fit if something is not the way he wants it. He insists on having Carol be he server everyday.
Melvin's behaviors sometimes limit his abilities to function. For example, he doesn't eat when Carol missed a day of work and he showed up at her house asking her to come back to work so she could serve him and he could eat. This limits him so much that he takes extreme measures to get Carol back at work....