It's called
"Exhibitionism"1. For some offenders, it’s a mental illness and the thrill of it is actually in watching the ‘facial expression’ after getting caught “choking the chicken”.
Links:
http://exhibitionistpost.com/
http://en.wikipedia.org/wiki/Exhibitionism
2. Others are just being naughty. That these cases seem to be on the increase suggests these guys have an acceptable success/conversion rate....where they find a willing/passive “participant” or are able to get away with it. Failure to “raise alarm” out of fear and/or embarrassment probably encourages this behavior.
3. This might be controversial, but if you could get time-series data on the minimum amount of cloth/fabric (square metres) that has (i) been
"considered acceptable for purposes of covering a woman’s body” or (ii) that has constituted “Kenya Uniform” for Nairobi and then run a regression with data for number of sexual offenses reported in the same region for the period….... well you wouldn’t be too surprised by the results. (of course there are other variables involved)
....For example, when was the last time you saw someone in a petticoat or "Mother’s Union" undergarments? Nowadays it’s all about plunging necklines and showing some flesh (don't use weather as an excuse, Arabs live in the desert). "Men" that have poor oo zero skills in courtship are bound to resort to other ways to gratify themselves including but not limited to the subject of this discussion. Please note that I am not speaking for them.