The definition of degrading has many ways of defining it but one of them is "to bring to low esteem" which means it would take a girl to not enjoy a certain sexual act in order for it to be logically degrading.

Therefore I find nothing in a sexual manner I'm willing to participate in as degrading but an opinion of another person may be different and seen as degrading in their own eyes.

So really there's no real answer to whats actually degrading. It's just a personal opinion that would basically reflect upon how a person may feel if they were involved in that act that may cause lowering the self esteem.