When they add another store mount.
Back in 2009 I was on my Alliance Paladin… And this massive Horde raid keeped ganking me for hours.
And whats worse a few days later one of the people from raid keeped attacking me all over Northrend.
Eventually just got so fed up I stopped playing for like a few days. Point of Story this is where my hatred for the Horde started and lasts till this day.
The day AQ-40 Ended and the Naxxramas Event Started.
Then there was a moment during Zul Gurub when all of a sudden every town and every city was dead from the plague 
Vanilla, realizing the whole “adventuring game!” thing was a lie, instead all there was to do was raid at level 60.
This messed me up too lol…
When I learned what Thaddius was made out of and why the screaming stops when you get to him.
My stomach churns a little now every time I run Naxx.
Desolate Council being Massacred by the Dark Rangers, and that one witnessing what happened in that Village in Stormsong where many innocents were attacked and killed for something they’ve had nothing to with.
I thought nothing in wow could scare me, however seeing that child crying over his deceased mother frightened me in a entirely different way.
The “death of a friend” quest series in Swamp of sorrows has always made me sad on both factions.
On Horde watching Neeka say goodbye to Helgrum as he died really made me shed a tear the first time I went through those zones. Orc’s are my favorite race too. it really broke my heart.
For Alliance Anchorite Avuun watches Magtoor die and Velen appears and gives a little speech. It made me really fall in love with Velen as a character. It was nice seeing a faction leader come all that way just to give comfort to someone dying and his friend.