Chelsea Handler has taken potty humor to a brand new level.
"She is just so ridiculous," Witherspoon, 35, tells iVillage. "She always threatens to tape record me when I go to the bathroom because I have a microphone on. I purposely take off my mic and put it somewhere else when I have to go somewhere. But she caught me singing a Rihanna song backstage."
Despite Handler's antics, Witherspoon says the comedienne -- who also counts Jennifer Aniston and Charlize Theron as BFFs -- is "very sweet."
"She's a really great friend. She's the kind of person who will cancel all her plans if you're in a bad mood and you just want to sit on the couch and watch a movie," Witherspoon says. "She's really generous. She likes to give a lot of good gifts!"
Handler isn't the only celeb Witherspoon admires. "I love Gloria Steinem. I think she's incredible," says the actress, who lists Holly Hunter, Frances McDormand and Diane Keaton among her faves. "[I respect] women who've really had long and wonderful careers where they create great characters and just seem to be endlessly interesting and fascinating to watch."