David Lee Roth -- Concert Scalper

David Lee Roth ain't talking 'bout love ... he's talking about the his new Mr. Clean image -- which he proudly put on display Saturday night during a surprise performance.

The Foo Fighters put on an epic show at The Forum in Inglewood ... featuring Alice Cooper, Paul Stanley, Slash, Joe Walsh and more -- but the highlight was clearly Diamond Dave.

The Van Halen front man played two of the band's classic songs ... and near the end of "Panama" he took off his hat to reveal the new q-tip on his head.

We'll never forget these luscious long locks.