Final answer:
The person who taps their fork against their plate before eating is likely to be suffering from a type of anxiety disorder related to an eating disorder, which could be indicative of obsessive-compulsive disorder (OCD).
Step-by-step explanation:
A person who feels the need to tap each forkful of food against the plate three times to be sure it is safe to eat would most likely be diagnosed with a form of an anxiety disorder that may be related to an eating disorder. This is not one of the options provided, but the behavior described suggests the person may have obsessive-compulsive disorder (OCD), which is characterized by repetitive behaviors (compulsions) that an individual feels driven to perform in response to an obsession, typically aimed at reducing anxiety caused by the obsession. While not explicitly mentioned in the original set of options provided, OCD is a mental illness that can indeed involve eating behaviors as part of the compulsions.