[ISL]

The "list" is self-organizing. When nobody listens to a purveyor of a poor theory, the proponent casts an ever-wider net.

Eventually, they have the bright idea to scrape the web pages of physics departments for emails. At least in my case, they started sending email within a few months of starting grad school.

The truly ambitious can decide to simply show up at the lab/building. A common refrain is, "here is my theory, tell me why it is wrong". No amount of countervailing evidence will be sufficient, usually because such a person will have critical misunderstandings of a fundamental concept or three and an intuitive sense that they are correct.

Don't invite them into your office and attempt to help them resolve said misunderstandings in a youthful desire to save them from wasting their time; they might not leave. Do, however, give them the references they might need in order to see the light.