I don't think anyone will disagree with this simple definition of a likely "rat rod":

If it's got shiney paint, it probably is not a rat.

If it has a flat, or faded finish it might be a rat.

If it is built with '50s influence, such as vintage parts, and pinstriping, it is very probable, that it's a rat.

If the owner has tattoos, or piercings, it is a 99% chance it's a rat.

The last 1% depends on the owner's description of "said vehicle". :-)~