Chris Brown better watch his back at the Grammys on Sunday . . . because superstar '90s balladeer Richard Marx might just be "Right Here Waiting" . . . to BEAT HIS ASS.  (???)

Marx recently added himself to Chris's long list of enemies when he Tweeted this . . . "Risque clothing banned at Grammys but guys who beat up women?  Come ooonnn downnnnn.....#goodcallgrammys."

For all you post 90's music kids asking who the heck is Richard Marx. He was a popular 90's Singer that was the first solo artist to have five number one singles. One of his more popular songs was 'Right here waiting for you"