How can I stop this Filipino guy from doing this to my Indonesian female friend?

Here in Makati, Philippines, a 27-year old poor perverted strong Christian Caviteño Filipino boy keeps on slapping the butt of my 27-year old Muslim Indonesian female friend because he is attracted to her and she wears a Sarong Kebaya. What should I do?

I am a 28 year old Indonesian male who is currently in Makati, Philippines.
How can I stop this Filipino guy from doing this to my Indonesian female friend?
Post Opinion