Gausha -- who boxed in the 2012 London Summer Games -- started wearing the American flag on his boxing trunks after his Olympic run ... but told TMZ he's done with that now in the wake of Zimmerman's acquittal in the killing of Trayvon Martin.
The Cleveland native added, "How can I wear my stars and stripes proudly in a country where they make a big deal out of Mike Vick fighting dogs; but not a young innocent black male's life."
Gausha added, "When I represented my country in the Olympics I was proud to wear my flag. I even wore it on my head on the way to the ring. What happened this weekend was a slap in the face."
Ironically, the African-American fighter made his professional boxing debut as part of a "Red, White and Blue Night" last November.
Gausha — who is 4-0 as a pro —isn't eligible for the U.S. team in 2016 — but it doesn't sound like the 25-year-old middleweight would be interested anyway now. He told TMZ he refuses to rep a "nation with so much racism and hatred."