Columbus. March 2008. UFC 82. A unification bout between Pride & UFC champions. I'll always remember Anderson Silva getting controlled & stifled by Dan Henderson in round one. Then he came out in the second round on fire, landing a front kick to the throat before eventually tapping Henderson with a RNC.
Other memorable in person events:
Seeing Rousey/Tate 1. We all thought she broke Meisha's arm.
Dan Henderson destroying Feijao.
Cleveland. September 2016. The arena erupted when Stipe knocked out Overeem. But the highlight for me was seeing Werdum front kick Edmond, post fight! He should've recieved a bonus for that alone.