Never deny a rumor
The best way to authenticate a rumor is to deny it. People want to believe they have heard a secret. If you deny it, they believe it. It's a secret.
When you hear a rumor about you...
Rumors are usually wildly unbelievable. When you say, "Yup that's me!" then you remove the mystique of the rumor. It is no longer sexy. When you vigorously defend, you reinforce the mystique.
Another method to debunk rumors...
Laugh! Say something like, "Wow, no kidding. I wish that were true. I would be the coolest person alive." No one wants to be ridiculed. Don't practice this at home.
An effective counter-attack...
Deny a rumor about some bully. You say, "You know I heard that Gigletybumps fries earthworms for breakfast. But I don't believe it. It couldn't be true, could it?"
Disinformation is what this is called.
Did information is rampant today and it will be worse tomorrow. In my youth disinformation would not spread beyond the 300 people in my high school. Now it can reach every corner of Earth.