Best response: Find, or better yet, make a “rainbow flag” with magic markers, bring it out to where they are stomping on the American flag, and start abusing their rainbow. Be sure to video their hissy-fit.
We have a local black minister promoting Blacks flying the Black Liberation Flag this July 4 instead of the Stars and Stripes.
In true ‘create controversy’ mode one of the local TV stations (maybe all) are running the story and interview at each news broadcast.
https://en.wikipedia.org/wiki/Pan-African_flag#/media/File:Flag_of_the_UNIA.svg