Why is train watching called that?
Foaming is an act carried out by foamers, who set a precedent long ago that railfans and all hence will drool, or foam, at passing trains. 
This was covered in another forum, but it has more to do with the behavior and attitudes of some railfans, then the attitudes or behavior of the regular railfan.
This subject has pretty much been beaten to death on this forum, all this thread is going to do is reignite the same old debate/argument/name calling that has gone before.
So, before this thread takes on a life of it’s own, just do a search for “foamer” in the forum search, and read the past ones…
A foamer is the type of rabid fan that rail types refer to as an “FRN” - ------- rail nut (figure it out). The kind of person who will trespass on railroad property “knowing” they won’t get hurt, the kind who interferes with rail workers by stopping them to make small talk, the kind who will climb on, under and over equipment, the kind of ‘railfan’ who gives ALL railfans a bad name in the eyes of some rail workers.
This thread is givin’ me that old feelin’, man …
Drooling on the track isnt allowed, it creates a wasted sand application. =)
[(-D]
Some folks are just plain too sensitive. I am personally both a sales person and a railfan, and I DON’T mind being called either a “peddler” or a “foamer”, as I consider both to be badges of honor. “A rose by any other name is still a rose”.
I suppose it depends a lot on the context.