Point of clarification: no one in this picture is actually engaged in the above-mentioned activity, but someone uttered the phrase and I don't know who(m). I just know that I haven't heard it in many many years, which puts it in the category of foundation garments (see below somewhere) and which I think is loaded with humor. Nowadays of course nobody thinks of it as a "dirty deed", any more than taking a picture with your cell phone is. There's a dumb-looking gesture, someone holding up their little phone in a jarring juxtaposition of ambiences. If there were any justice, there would be a law that those teeny cameras could only be installed in shoes, so people would have to hold up their shoes to take these pictures that they just have to have. Or better yet, underpants! If you had to hold up a pair of underpants every time you wanted to take a damn picture, there'd be a lot less of that particular activity going on in public. And probably a slight increase in dirty deeds.