Ex-Texas hoops star center Jaxson Hayes got himself a sick pre-Draft gift that would make Homer Simpson proud ... immortalizing his "Sideshow Jax" nickname in diamonds with a Sideshow Bob chain!!
TMZ Sports has learned ... the projected lottery pick wanted to treat himself before the biggest day of his life ... hitting up Al the Jeweler of LaBelle Jewelry in NJ to hook him up with a chain of his Simpsons character Doppelgänger.
Al -- the go-to jeweler for huge stars like Jarvis Landry and Stefon Diggs -- tells us the one-of-a-kind piece is made of VS diamonds and rubies .