Parents, you are sort of on the safe side, The lyrics are in Korean, so kids will not likely understand the lyrics and think of flirting and PSY hitting on girls, so they don't see what the song really means, and the song means some weird stuff iffy for 9 and lower. There is one use of "sexy", but if you remind your kid not to repeat and tell him how sometimes it could be rude and inappropriate in school, they might not use it and they might ignore the word. There are clean versions avaliable which take out "sexy", but I don't see the problem. They will love seeing PSY rock to 1 billion and copy his "dance moves". The dance moves actually mean something hidden, if you know what I mean, so tell your kid 8 and under not to dance like PSY does. In some cases, the music video has people dancing on top of people squatting up and down, which is very inappropriate, so it looks "wrong" and I agree, I just would let 10+ see the music video, 8+ listen to it. The main points are just one word and the music vid. Otherwise, it's PSY's catchy tunes.
What other families should know
Too much sex
Too much swearing
Too much drinking/drugs/smoking