I have been known to shout ‘For yoo-hoo!’ whenever someone in the party summons their Steward.
I also enjoy Denathrius lines, but that’s a given at this point. My favorite is ‘I am Revendreth!’ in phase 3. We had tons of laughs on farm repeating that line in different voices. You haven’t lived your life until you’ve heard people claim they’re Revendreth in thick regional accents, in a Mickey Mouse voice or in a Bane voice.
Other than memes and jokes, nothing really stood out so far. In Legion we had some cool Illidan lines like the ones from Rejection of the Gift, BfA had everything around the Daughter of the Sea rhyme, nothing really catching the imagination like that in SL thus far. ‘He was my student!’ came close but it had such a weird delivery and so shoehorned into the conversations it crossed over into joke territory for me. Perfect line to shout whenever someone mentions Arthas, regardless of context.