Mean Girls star Rachel McAdams has explained why she turned down the opportunity to appear in a recent reunion with the cast.Lindsay Lohan, Lacey Chabert and Amanda Seyfried all reprised their respective roles from the 2004 film for a new Walmart advert, but McAdams’ Regina George was nowhere to be seen.Explaining her decision not to appear in the ad, the Are You There God? It’s Me Margaret actress told Variety: “I don’t know. I guess I wasn’t that excited about doing a commercial if I’m being totally honest.“A movie sounded awesome, but I’ve never done commercials, and it just didn’t feel like my bag.