When Justin Bieber talks about giving back, he's not just delivering lip service.

Take, for instance, yesterday, when a Yahoo editor happened to run into the Biebs at a pizzeria and witnessed some of the 'Home to Mama' singer's incredible generosity.

Taking to Twitter, she wrote:

But that wasn't all -- Bieber's random act of kindness caused a charitable chain reaction. Replying to a "thank you" from the Biebs, the editor continued:

While Bieber may get a lot of bad press for his various eyebrow-raising antics, there is no doubt that he has always gone above and beyond in terms of giving back since the beginning of his career. And yesterday -- Martin Luther King, Jr. Day -- was more than fitting to exercise some of that kindness and generosity.

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