LMFAO -- The $7 Million Lawsuit SURPRISE at 'American Idol'

By the look on RedFoo's face ... you wouldn't think he'd just been hit with a $7 million lawsuit ... but that's exactly what happened right as this photo was taken.

The LMFAO DJ was on his way into the "American Idol" set in L.A. yesterday ... when he got SERVED with a $7 million lawsuit filed by the band's former management company.

The management company is suing for breach of contract ... claiming it took LMFAO's career "from 0 to 60" ... only to be kicked to the curb when the big bucks started rolling in.

But RedFoo didn't seem too concerned when he got slapped with the suit yesterday ... smiling and laughing ... and then posing for a pic with the tattooed process server.