What can I, as a user, do about offensive reviews in App Store?
There is a direct way of reporting these concerns, although Apple does not make it obvious how to do it, unfortunately.

Go to the review in question and press &amp; hold (long press) on it, and you will see this pop-up:



Tap on "Report a Concern" and it will bring up this window:



"It contains offensive material" seems like an appropriate choice.

You will be given a text box to explain why you think it is offensive.

Can't say that anything will actually happen with it, but I'd wager it's the best chance you have of getting someone's attention.