USC: Chill Out Reggie Miller ... We're Not Sexist!

USC is firing back against Reggie Miller's allegations that the school has a sexist banner system in the Galen Center ... claiming it did NOT slight his sister Cheryl Miller ... and that Reggie jumped to incorrect conclusions.

Here's the backstory ... Reggie RIPPED the school on Instagram earlier today -- claiming a former male college basketball player was honored with his own banner while Cheryl had to share a banner with 4 other women.

"You guys should be EMBARRASSED and ASHAMED," Reggie wrote ... "Cheryl DESERVES her own wing at the Galen Center."

FYI -- Cheryl is widely considered the greatest basketball player (male or female) to ever attend USC.

But a rep for SC tells TMZ Sports ... Miller has the whole situation down wrong.

Turns out, the school customarily singles out past great athletes and TEMPORARILY honors them with a solo banner. It just so happens Gus Williams was honored earlier this month and his banner is still up. The solo banner will eventually come down and his name will be added to a group banner just like Cheryl.

So, chill Mr. Miller ... and in the meantime, enjoy some highlights of one of the greatest players ever.