One specific moment occurred during the recent "Big Four" tour with fellow thrash pioneers Megadeth, Anthrax, and Slayer, with all four bands performing a portion of Diamond Head's classic "Am I Evil?" on the same stage, in unison. To see these four bands actually performing in the same show together had to be something special, and a crowning moment for all involved.
Actually, it was only Metallica, Megadeth, and Anthrax playing "Am I Evil?" because the guys from Slayer were backstage editing their concert footage for the satellite broadcast.
The 1996 MTV Europe Music Awards, After being told not to use any profanity on the show, Instead of playing King Nothing as scheduled they instead played this.