An exchange of words

I have a tee shirt with the words “unfuck the world” on it. The other day, in the supermarket, a cop, stood next to me in the line, looked at it and said “You know I could nick you for that?” I could tell by his smile that he wasn’t being serious but, I wasn’t in the mood.
“I don’t think you could, actually.” I replied mirthlessly. As his smile faded, mine grew.
“Despite agreeing with the sentiment sir, your tee shirt is displaying an offensive word.” I knew I’d pissed him off, because he called me sir; my job was half done.
“Actually it doesn’t,” I informed him, “unfuck isn’t even a real word.”
“Yes,” he quipped back at me, “but it contains a real word within it, an offensive one.”
“So does Scunthorpe,” I pointed out, “what you gonna do, nick everyone in a Scunthorpe United shirt?” At this point he was called to the checkout but I could see him figuring it out, saw the moment of realisation dawn on his face.