I had to stop myself from laughing at that last line, but I understand you are frustrated on the one hand you are trying to promote the values of the school, but at the same time not act as a dictator to the students either. The other person seems to come from a very authoritarian old school of teaching. I think the best way to address this is with some discretion. Arrange a few minutes of one on one with the young ladies in question. Explain to them that if they dress in this way that the boys will treat them as no more than objects of conquest and not real human beings with ideas and intellect. Advise them that socializing at school is a secondary function and that most importantly they are here to work. This again should not be done out loud in front of other students. Humiilation is not a good way to dicispline young people.