In case you're not familiar with the term, a "foamer" is a person who is a big fan of trains. The term is derived from people who foam at the mouth when they see a unique train.
In the video below, this particular foamer thought he was about to see a Flying Scotsman, which is apparently a pretty special choo-choo. But it was all ruined, thanks to a stupid commuter train and some incredible timing! Poor fella!