Hey, it’s not harrassment until you start slipping dollar bills into the waist of their slacks. (And maybe not even then, if they appreciate the tips!) 
I remember the blouse effect when I was in Poland for a job. Young Polish women are gorgeous. On a sunny day, males would begin to congregate around the Marine post at the front entry to the embassy, which faced east. As the Polish nationals came in the door for work, the sun was at their backs, and the blouses were flimsy. Entertainment at its most base.
Huh. Dude, you say that like it’s a BAD thing. My suggestion is to immediately say something. If they increase their wiggling, it’s not YOUR fault, now is it? 