The OCD person has obsessions and compulsions. The photo above shows someone who has bitten their nails because of an obsessive compulsion. They may frequently feel they need to wash their hands, for instance, or may not leave the bathroom until they have ritually cleaned and rinsed their hands 10 times. There are things that they feel they have to do that to an onlooker doesn't seem reasonable. The television detective, Monk, has to touch every parking meter or lamppost as he walks by, for instance, and if he misses one, he must go back and touch it.
Melvin in "As Good as it Gets" has breakfast in the same restaurant every day, sits at the same table and has the same waitress. When someone else sits at what he perceives as "his" table he creates a scene because to him it is wrong to sit at any other table. The same when it is his waitress's day off, breakfast isn't right and so the whole day isn't right.
The whole issue with the OCD person is that other people perceive the behavior is controllable, but to the OCD person it isn't. They can't just hurry out of the bathroom because someone else requests it. Sometimes the obsessions come in the form of thoughts and the OCD person can't get a certain thought out of their head.
OCD often runs in families and is counted as an anxiety disorder. It can suddenly appear to come on, but often the roots are in the person's childhood. The behaviors are actually self calming, the more stressed the person becomes, the more the repetitive behaviors appear, but then they have a calming effect. Sometimes OCD can appear with other mental illnesses such as bulimia or anorexia.
Most people with OCD can't stand any sort of mess in their own homes or in other peoples. If they go in someone else's home that is messy, there is an urge to tidy it. The urge is so strong that it overtakes any social manners they may have.
Some level of OCD is in most of us, but it is when they obsessions get stronger and more frequent that an OCD diagnosis is suspected. Some people are so nervous about failing in public that they eventually refuse to go out. A diagnosis of OCD can only be given by a mental health professional. OCD can be helped with counseling, medication or behavior therapy. Mental health professionals usually take regular health insurance.