Ray J -- How I Celebrated Kim K's Wedding ...

While Kim Kardashian was trading "I Do's" in Montecito ... the guy who helped thrust her into superstardom was still taking credit for his conquest during a performance in Vegas ... TMZ has learned.

Ray J hit the stage at the Chateau nightclub in the Paris Hotel ... when people began asking him how he felt about his former sex tape partner's wedding.

A TMZ staffer who was in the crowd says Ray J simply smiled ... and quipped, "I did that."

Fans continued to plead with Ray J to share his thoughts on the wedding, but he wouldn't open up ... mostly laughing every time someone brought up her name.

Apparently, Ray J has moved on ... after his performance, he was getting up close and personal with a mystery lady.