it means the blue shirts

Yes they can. If they're put on flag poles!!! {LOL}

Because the T-shirt is, according to the Flag Code, indeed a flag, it leads to the somewhat absurd conclusion that it needs to be retired in a dignified way.

It is technically illegal to wear a flag, though many people wear flags on their shirts these days. I would not recommend wearing a flag itself as apparel as this could be interpreted as a rude, classless, and unpatriotic gesture.

One can find men's long sleeved t-shirts for sale online through eBay, Amazon, and Red Flag Deals. If online shopping is not an option, Wal-Mart or Sears usually have low-priced t-shirts on sale.