The musician made the vow after discovering his band had been mocked by their peer.
Speaking to the Daily Star about their third record, Scars & Stories, he said: "When we started making the album, I saw footage on YouTube of Brandon getting mad at a Killers crowd who were a little sedate. Brandon was yelling, 'Come on, stand up and dance. This isn't a f**king Fray show'."
The Denver group, best known for their emotive hit single 'How To Save A Life', plan to get Flowers back for his words.
"All I could do was laugh because that's true - we do have a very thoughtful, sensitive crowd who don't get to dance much.
"Still, I'll pay Brandon back for picking on our fans. Next time I see him I'll have to punch him in the mouth."
> The Fray "proud" of new album 'Scars & Stories'
> The Fray: 'Scars & Stories' - Album review
Watch The Fray's 'Heartbeat' video below: