Karma's OP. The most recent episode of the silly YouTube series "Heroes of the Storm WTF moments" begins with a cautionary tale of when it's acceptable to troll an opponent in-game.
Since you can't chat directly with your enemies in HOTS (League of Legends and Dota 2 both have cross-team chat functionality, for a point of comparison), the easiest and clearest way to send a message saying yes, I am indeed trolling you is to make your character dance.
And dance Zeratul did, right after the lithe StarCraft assassin killed the enemy team's King Leoric. Leo doesn't "die" the same way other heroes in HOTS die -- he turns into a ghost for a little while, unable to attack. So Zeratul stuck by the guy's inanimate spirit form, dancing his heart out while the guy watched, powerless to retaliate.
Thankfully, Leoric's old friend Diablo was available to pick up the slack: