As Good as It Gets (1997)

Melvin Udall (Jack Nicholson) is an obsessive-compulsive writer of romantic fiction who's rude to everyone he meets, including his gay neighbor Simon (Greg Kinnear), but when he has to look after Simon's dog, he begins to soften and, if still not completely over his problems, finds he can conduct a relationship with the only waitress (Helen Hunt) at the local diner who'll serve him.