I had one such moment when looking at Death Knight tank theorycraft recently.
I was looking at DK tank builds, and came up with a nice Blood/Unholy build. Then I popped over to Elitist Jerks to see how far off accepted theorycraft I was. I was surprised to the see that the suggested DK tank build went 6 points into the Frost tree to pick up Lichborne.
Spending 6 points to pick up a fear break seemed unusually situational to me. So I kept reading. And it turns out the real reason behind Lichborne is kind of cool.
Lichborne turns you into an undead for 10 seconds. Death Coil can be used to heal undead. And [Glyph of Death's Embrace] makes the heal very cheap.
It all gets combined into a macro that essentially turns Lichborne into a quasi-tank cooldown, helping the DK to heal herself back up after a big hit:
/cast [@player] Death Coil
Pretty clever, in my opinion. A moment for Johnnies to appreciate.