Renée Zellweger's On-Air Explosion

By David Caplan

08/21/2009 at 07:30 AM EDT

Renée Zellweger vented her frustrations by taking aim at a guacamole-filled piñata during Thursday's taping of the Late Show with David Letterman.

Zellweger – looking buff in a blue dress – and Letterman took to the brightly colored cardboard object after the Oscar winner talked about Blue Parrot, a Mexican restaurant in East Hampton, N.Y., where she is a partner along with Jon Bon Jovi and others.

Not mentioned, however: her recent outings with beau Bradley Cooper.

"I've been all over the place," Zellweger, promoting her new movie My One and Only, told Letterman. "This has been the summer I've been catching up. You know you say, 'One day I'd really like to ...?' I've been doing all those things. I finished filming in January-February. And I've been running around since."

As for her business venture, she said, "And you know you say, 'Oh, it would be fun one day to open a restaurant?' So I did! I like a good taco … and being a Texan, I'm very critical of guacamole!"

The actress, 40, and the TV host, 62, then proceeded to act like kids and attacked the piñata, until it crashed to the floor and guacamole came spilling out. Asked a giggly Zellweger, "Where are the chips? Where are the chips?"

RELATED GAME:
• See Renée's extreme movie makeover in Celeb Concentration!