I guess black boxer briefs could be worn over the top of other clothing, Superman style...
I am in the US for a couple of weeks- bought black protest T shirts for the whole office from Amazon that I will be bringing back...maybe I need to bring an extra suitcase of black clothing back for protesters...
Amazon has a lot of good designs (I got the relatively tame "hong kong" in one direction in Chinese, "add oil" when you turn it 90 degrees) but kind of pricey.
Guess I could bring back plain black T shirts from somewhere cheap (Walmart, I'm looking at you) and get them printed in HK? Or is the printing done only in mainland these days?