Rachel McAdams is giving the 411 on why she did not appear in the viral Black Friday Walmart ad that reunited most of her “Mean Girls” co-stars almost 20 years after the iconic 2004 film debuted.

The “Are You There God? It’s Me, Margaret” actress told Variety that a commercial wasn’t her “bag.” She also was unaware that her former co-stars were appearing in the campaign. Lindsay Lohan, Amanda Seyfried, and Lacey Chabert were back as the Plastics, with each characters’ storyline leading back to North Shore High as a direct sequel to the movie.

“I don’t know, I guess I wasn’t that excited about doing a commercial if I’m being totally honest,” McAdams said. “A movie sounded awesome, but I’ve never done commercials, and it just didn’t feel like my bag.”

McAdams continued, “Also…I didn’t know that everyone was doing it. I would, of course,...