Republicans already do this with their swimwear.
Guess they were ahead of the curve for once.
For the traditional law and order crowd (not so sure now) wearing anything the US flag is unlawful until 1989 but now is still considered poor Etiquette and rarely acknowledged as such.
Also, the flag code is merely suggested standards for how to care for the Flag, and not a law that citizens must abide by. To go further, there is distinction between the flag, and flag motifs. Flag print toilet paper, totally okay, flag print jockstrap, totally okay. Taking your purpose made American flag, and wearing it as a cape, not okay. Wearing an American flag print towel as a cape, totally okay.