Foamer

Foamer is North American railroad-employee slang for a railfan — almost always used by professional railroaders rather than by fans themselves, and almost always with a wry or mildly disparaging tone. The origin is the unsubtle image of someone literally foaming at the mouth when a desirable locomotive comes into view: rare paint, a foreign visitor, a heritage unit, a freshly-painted leader. Crews on the ground use it the way other professionals use private slang for civilians who don't understand what the work actually involves.

Within the railfan community itself the word is more contested. Some fans embrace it ironically — "yeah, full foam today" after photographing a rare consist — while others reject it as insulting or as an insider term that doesn't belong outside the cab. Online forums have argued the etymology, the appropriateness, and whether self-application is permissible for decades without resolution. Other communities have their own equivalents: British enthusiasts speak of gricers, Australians sometimes use "gunzel," and continental European fans tend not to have a comparable single-word slur because their hobby is less culturally marked.

Most reporters and editors avoid the term in formal writing because of its dismissive register. If you're writing about the hobby publicly, "railfan," "trainspotter," or "rail enthusiast" are the neutral choices; foamer is best reserved for in-group conversation where the irony is understood.