Credit: Kevin Winter/ACMA2011/Getty Images

Maybe Taylor can write a song about this!

Reese Witherspoon and Taylor Swift lunched at Los Angeles' Boa Steakhouse on Aug. 26 -- and chatted about their shared ex, Jake Gyllenhaal!

"They talked about how vain and self-aborbed Jake can be," a source tells Us Weekly. "They laughed about it."

(Gyllenhaal, 30, dated Swift for two months in 2010; he and Witherspoon, 35, spent two years together before calling it quits in late 2009. Witherspoon married CAA agent Jim Toth in March.)

The blonde Tennesseans first bonded at the Academy of Country Music Awards in April and had planned to hang out.

And it looks like this relationship may last. Swift, 21, invited the actress and her kids to an upcoming show, and Witherspoon gave the singer a lift home after lunch!