Mine would have to be not a single moment but one that was spread out over three days. 1990 when we beat #1 Missouri on Saturday 107-90 then turned around and beat the new #1 team, Kansas, on Monday night 100-78.
We not only beat those two teams but beat them silly. To this day nobody has beaten the #1 back-to-back and probably never will. I have never heard the LNC as loud as it was at those two games.