sadly, your probobly right.
wolf-whistling cannot be made illegal, then your into the area of free speach, part of that deal is some things will offend, like somali emams extoling the virtues of FGM or right wing preachers burning Qorans, both hugely offensive but you cant legeslate against bad taste.
but pinching a bottom is assault, and the police should take that seriously, not giggle thinking it isnt inportant. what makes one person think they can do that to another stranger? what sort of entitlement must he feel to think he just can?
did you go to the police ? or did you think they wouldnt have taken it seriously? ( i do think they probobly wouldnt have).