Matinee idol Freddie Prinze Jr. won't dish about his impending nuptials to Buffy the Vampire Slayer's Sarah Michelle Gellar — "We never talk about the personal stuff" — but ask him about setside horseplay on his baseball flick, Summer Catch (opening Friday), and you'll get an earful! Let's just say, the 25-year-old gives new meaning to the term "man-child."

Having heard about the pranks Prinze pulled on previous co-stars Julia Stiles and Claire Forlani, Catch's Jessica Biel (7th Heaven) was ready to rumble. "Believe me, I was in the mindset that I was going to get water on my head or mud somewhere — but he didn't do one thing to me," a disappointed Biel tells TV Guide Online. "Maybe he knew I would retaliate somehow."

Indeed, Prinze has learned it's better to choose his battles. "I try to take it easy on the girls now," he says. "I get the guys. I have more fun doing that."

Of course, that depends on your idea of "fun." After a long night of shooting on the baseball diamond, Prinze reveals that he attached an athlete's electric muscle stimulator to co-star Jed Rhein's leg while he was sound asleep. "I turned it on and his leg twitched a little bit, but he didn't wake up," Prinze gleefully recalls. "So I turned it up more, and his face starts twitching. I'm hysterical laughing — and laughing loudly — and he's not waking up. So I crank it up, and his whole body starts shaking and he just freaks! He's running around screaming at me, 'I dreamt I was dying!'"

Rhein shook off the shock treatment, but gave Prinze the cold shoulder for three days afterward. "I did a couple of other [pranks], but that was the funniest," he admits. "But Jed didn't like it." Note to fiancée Sarah: Keep a close eye on the household appliances.