In the days leading up to the 1989 game, Billy Brewer was said to have showed his team a t-shirt "printed in Starkville" that mocked Chucky Mullins in a particularly cruel way--all as a motivational technique. The local t-shirt places in Starkville learned through professional relationships that a UMiss grad assistant brought the design to an Oxford screen print shop for the single shirt to be printed.
In other words, it's all run-of-the-mill rivalry stuff.