Miss USA Nia Sanchez -- STREET TAEKWONDO ... This Is How I Fight Off Creepers

Miss USA has a helluva way to deal with creepy weirdos who try to get too touchy-feely with her -- SHE BEATS THEIR ASSES!!

Turns out Nia Sanchez -- the reigning Miss USA -- happens to be a 4th degree black belt in taekwondo ... who trained for more than 10 years!!

And when we saw her out leaving Cipriani Wall Street in NY this weekend -- she demonstrated how she uses her training when some guys try to get a little too close. She's kind of a bad ass.

Don't worry, the guy in the video isn't one of the creepers Nia's talking about, he happens to be her good friend.