"He's my boyfriend!" she said. "It's new and it's fun. It's nothing too serious, I don't want anything that's going to take up so much of my energy and time right now in a bad way. I just want to have fun, that's what it's about."
While Rihanna and the Dodgers star are keeping it casual, one of the singer's famous friends is making a serious commitment - Katy Perry is marrying Russell Brand, and Rihanna said she's in charge of the bachelorette party.
"She put that on me next week," Rihanna said. "I have to come up with something cool because she's getting married in India so I'm like, 'Now what do I do to match that?'
As if that's not enough to handle, the singer is about to head out on her first major headlining tour (with opening act, Ke$ha, see tour dates below), having appeared on "American Idol" on Wednesday night with a taste of what's to come.
"It was a little sneak preview of what you're going to see on tour," she said, describing her show as a story in five chapters. "It's a whole rollercoaster."
While Rihanna strapped on an electric guitar for her "Idol" performance of new single "Rock Star 101," she told Ryan she's been getting some rock star 101 training herself - from blink-182 drummer Travis Barker.
"I always wanted to learn how to play the drums and I started talking about it, I did an interview, and he saw the interview and said, 'You can't have anybody else teach you,'" she laughed. "It's so difficult! It's a lot of coordination - I thought I [had that] until I started playing drums. [But] he makes it really clear to understand."
The svelte star said she's also trying to slim down for the tour, but admitted one thing might be getting in the way.
"I hate healthy food, I'm just going to be honest," she said. "It has no taste. I'm from Barbados so everything has extra flavor, extra salt."
RIHANNA LAST GIRL ON EARTH 2010 NORTH AMERICAN TOUR DATES
Jul 02 Seattle White River Amphitheatre
Jul 04 Vancouver General Motors Place
Jul 06 Calgary Pengrowth Saddeldome
Jul 09 Sacramento ARCO Arena
Jul 10 Mountain View Shoreline Amphitheatre at Mountain View
Jul 14 Albuquerque Hard Rock Casino Albuquerque presents The Pavilion
Jul 15 Denver Comfort Dental Amphitheatre
Jul 17 Las Vegas Mandalay Bay Events Center
Jul 21 Los Angeles Staples Center
Jul 22 Phoenix Cricket Wireless Pavilion
Jul 28 Atlanta Philips Arena
Jul 30 Tampa Ford Amphitheatre
Jul 31 Miami American Airlines Center
Aug 03 Indianapolis Verizon Wireless Music Center Indianapolis
Aug 05 Toronto Molson Canadian Amphitheatre
Aug 07 Montreal Bell Centre
Aug 08 Boston Comcast Center
Aug 11 Uncasville Mohegan Sun Arena
Aug 12 New York Madison Square Garden
Aug 15 Wantagh Nikon at Jones Beach Theater
Aug 18 Camden Susquehanna Bank Center
Aug 20 Bristow Jiffy Lube Live
Aug 21 Hershey Hersheypark Stadium
Aug 22 Detroit DTE Energy Music Theatre
Aug 25 Chicago United Center
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