The fans of On the Waterfront are people who like movies on TCM and the Criterion Collection. It's not a fandom where people dress up like Terry Malloy or Father Barry for Halloween. No one would know who you were—unlike, say, if you dressed up like Chewbacca.
But the movie has fans. The line, "I coulda been a contender" has been repeated over and over again, recycled through all of pop culture. The American Film Institute said it's the third greatest movie quote of all time, just beating out "Toto, I have a feeling we're not in Kansas anymore."
Washed-up boxer: 1. Dreamy young farm-girl with snazzy shoes: 0.
Actually, Shmoop itself already has a pre-existing analysis of the quote. Robert DeNiro basically repeats the whole famous speech all over again in the movie Raging Bull, which is just as big of a classic as On the Waterfront. It's an example of the movie's ongoing influence.
DeNiro's character, boxer Jake Lamotta, gives speeches from famous movies at the nightclub he's running. His version of the On the Waterfront speech adds an extra-layer of irony. Unlike the fictional Terry Malloy, Lamotta really was a contender, and a great boxer—but now he's been washed up and forgotten. It's a new twist on a famous line.
Also, the director of Raging Bull, Martin Scorsese, is a huge Elia Kazan fanboy. He actually made a documentary in tribute to Kazan, entitled Letter to Elia. He probably signed the letter with a little illustration of a heart with the words "Elia & Marty 4EVA" in it.
If Martin Scorsese loves your movie, no one can say you don't have some serious fans.