Why did Rain call Lee Joon 'darling'?

On the most recent episode of KBS 2TV Happy Together Season 3, MBLAQ's Lee Joon and Rain were both featured guests. The two shared many stories about each other, and Lee Joon did not hesitate to share a hilarious story about his boss, Rain. Lee Joon said, "Something really shocking happened. I went to Cebu with Rain for a photo shoot and afterwards, we decided to go swimming." "I was resting in the corner of the pool in a lounging area, and Rain popped out from the water. Like a scene from a movie, he stroked his hair back, looked at me and said, 'Darling'." Lee Joon continued, "He kept smiling and calling me, 'Darling~ darling~ darling' continuously so I got really shocked. He has such a scary and charismatic image, and so I still don't understand why he did that." After the set settled down from the explosion of laughter, Rain explained, "I have called him 'Darling', but I didn't mean it that way." Then he soon changed his mind and said, "Actually, I have short-term memory so I don't remember saying that." Lee Hyori, who was also a guest on the show said, "Do you call your girlfriend 'Darling'?" To this, Rain admitted, "I have called my ex-girlfriend 'darling'." Can you imagine seeing this hunky, charismatic man putting his charms on and saying 'darling' to his girlfriend? It's an interesting sight indeed! http://www.youtube.com/watch?v=DZfheJv0Aio