A 21-year-old unmarried man has near-daily intrusive thoughts that his neighbors knock on his door at night. He tells the PMHNP he knows this knocking is just his "imagination" because the neighbors work nights and are not home. However, he feels compelled to get out of bed and open the door, no matter what time it is. He opens and closes the door repeatedly for at least an hour, sometimes longer. He says he has had this problem "in the past" and did not seek help for it. This time it has been going on at least 6 months and is becoming "problematic." It is interfering with his ability to get a good night's sleep and he is having problems at work. His roommate is also very troubled by it. The PMHNP will diagnose him with which of the following?