This opening was made controversial when so called "concerned viewers" or perhaps, some Party Pilipinas detractors reported to MTRCB that it was not "wholesome" for kids. It's precisely the reason why it is classified for Parental Guidance, the show is not for kids. TV is not for kids alone. It is for adults too. I don't think kids watch Party Pilipinas. They watch cartoons. I have observed kids in the house. They are not just interested.
I didn't see anything wrong with the opening number. An open and broad-minded person would just find it a simple entertaining number. It's just one of those. The narrow and crooked-minded person, however, would see otherwise. Whatever it suggests is all in the mind of the viewer.
The irony is this. If a viewer finds that number offensive, he or she is simply projecting what he or she has been hiding all the time. How he or she perceives it reveals the "dirty" secret that he or she has been keeping.