Straight: Bob single-handedly save the passengers of an out-of-control train. When the news reporter claim him a hero, Bob utter this trope.
Exaggerated: Bob single-handedly save everyone on the planet from a certain death by meteor crash. When the news reporter claim him a hero, Bob goes on a long rant explaining why he's not a hero.
Downplayed: Bob single-handedly saved the passengers of an out-of-control train. When the news reporter claim him a hero, Bob says that it's because he has the competence to do so and it doesn't come out as boasting.
Bob is a humble person.
Bob is a beta- or even omega-type guy.
Bob doesn't like the responsibilities that will inevitably come to heroes.
Bob had legitimately self-serving motives for his seeming act of heroism, and spells them out in no uncertain terms. He didn't care if a bunch of complete strangers lived or died as a result of his actions.
Inverted: Bob is caught dooming the passengers to a burning trainwreck. When the torch-and-pitchfork mobs come at him, he say "No, I'm not a villain. I Did What I Had to Do." The other option was endangering the lives of people on the route of the train.
"I'm not hero, I'm a SUPERHERO. Write THAT down in your newspaper!"
When Bob rescues Alice from her kidnappers, Alice calls him a hero. Bob tells her that he is not one, and then takes her back to the kidnappers telling Alice that he: "warned her"
"...is what I'd like to say, but I guess anyone will do what I do if they were in my position. Think Nothing of It."
Parodied: "I'm not a hero, I'm just a social reject with no jobs, no money, no hope of the future. This is just a momentary flash of altruism in the infinitely cold darkness that is my life. Now if you will excuse me, I'll cut myself."
Zig Zagged: ???
No one acts like a hero, no one can praise them, and thus no one can deny the claim.
"You're a hero, Bob!" "I... guess I am, aren't I?"
Enforced: An Aesop, either about humility, or about being proud of your achievement.
Lampshaded: "You don't seem to be the flashy type."
Defied: "I'm not a hero, I'm-" "He's the hero, folks! Give him an applause!" "Yeah! Bob is the man!" "...Guess I'm the hero."
Discussed: "I suppose I'm have to say I'm not really a hero even though I slew thirty dragons singlehanded and rescued the World's Most Beautiful Woman from the Evil Overlord. That's what every other hero does."