As I don't understand Korean, I have no idea what the pop star Psy means by "gentleman." His video for "Gentleman" illustrates a goodly number of pranks no gentleman should ever do. The stunt with the treadmill was particularly mean and dangerous.
However, the appearance of the portly pop star on MTV is my big treat when I am on the treadmill at the gym, so here is his silly video. As there is much clothed-yet-lewd behaviour with telephone poles, it is not safe for little brothers. (Actually, nothing in this video is safe for little brothers, since Psy acts like the world's naughtiest 10-year-old.) The Korean dancing girls are less trampily dressed than the usual women who wiggle across the TV screen, though.
Update: I had a look and although the lyrics--I have a hard time hearing lyrics without having read them-- are not entirely innocent, he is singing "I'm a mother-father-gentleman."