When you're working hard, you only have time to mind your own business.
These days it seems there's a lot of people who think it's their job to stick their nose in other folks' business. Most of them are passenger seat doctors or half-assed amateur politicians. A steady Rx of ass kicking may set them straight, but so will a little bit of hard work. When you're working hard, you don't have time to pay attention to anything else but getting your tasks accomplished.
Most of those people are afraid of hard work; and this shirt isn't made for them. It's for hard working individuals such as yourself that don't mind getting your hands dirty and won't go looking for a pat on the back when the job is done.