Back in HW, when I was still a noob, I once forgot to equip a shield before doing a 8-man fight. Not forget a CD. Forgot the friggin shield, as a PLD.

I don't know how it happend, I just know it happened and I didn't even took notice of it until someone in chat asked "Uh... where is your shield?". I felt so bad, not helped by friend in voice chat laughing at the error, but finally laughed with them. It fortunately was to no consequence as I was OT and it was Gilgamesh, so not a hard fight, but I still look back at this moment as my moment of shame as a Tank. A bit fondly nowadays, I must admit.