"Sexting" is trendy and controversial. Sending sexually explicit photos and messages over the phone has gotten some celebrities into trouble. And David Letterman isn't a fan -- he doesn't get the whole "sexting" thing. Luckily, Sean "Diddy" Combs appeared on 'Late Show' (weeknights, 11:35PM ET on CBS) and helped Dave out.

Combs and Letterman discussed the recent Brett Favre scandal, in which Favre was accused of sending photos of his private parts to Jenn Sterger, a sports reporter and model. Dave was confused, so Sean smoothly explained how to go about "sexting" someone. "I'm the perfect spokesman," he said. "I'm a sex-texter myself."

"This an art," Sean told him, "that men and women have had since the beginning of ... 'mobile devices'." He then defended Favre's right to send a picture of his "penis" -- causing the host to choke and cough in embarrassment. Next, the rapper gave Letterman some helpful hints. According to Diddy, one can use new phone technology to make your "size and width" seem larger.

But Dave didn't want technical advice. He had a problem with "sexting" in general. "I don't even want to see a picture of my 'thing,'" he said. But at this point, the talkative Mr. Combs fell silent. After a pause, he said "I think maybe we should change the subject."