D.Va, due to being a pro gamer, is sometimes seen by fans as trolling and berating her opponents much the same way real-life players of online multiplayer games do, especially when she's drawn by fans in her "Gremlin" form.
Tracer also lends herself to this due to her harassment-oriented style of play, her accent (it isn't unheard of for some of the less-serious fan works to portray her as a babbling maniac who speaks entirely in impenetrable English lingo) and her near-constant giggling. It helps that her canon personality isn't too different, since she's a bit of a joker who loves messing with her opponents.
Gameplay:
Bastion, due to its appearance basically securing Play of the Game for whoever's playing as it (at least initially). Many players joke about how Bastion is a salt-powered robotnote "salt" being slang for anger, usually of Sore Losers.
Mei has become infamous for inexperienced players or Griefers using her to recklessly place ice walls to block her own team's attacks, or even block off spawn room exits.
Tracer can be this as well sometimes, giggling and spouting cheeky English lingo to annoy other people as she hits them from the sides and vanishes before they can counter. It doesn't help that one of her unlockable POTG animations depicts her laughing, a strategy often used by Trolls to ridicule their victims.
The Random Number God for Loot Boxes. If it's not Common-Common-Rare-Common, it's Common-Common-Legendary-Common…but the Legendary is a duplicate. Or cash.
The Play of the Game generator gets this on occasion for its tendency to ignore legitimately good plays in favor of laughable plays such as the aforementioned shots of player corpses and other ridiculous moments.
Sombra quickly became this upon her introduction proper, thanks to a combination of her dragged-out ARG, the Infiltration short showing her messing with Reaper as he tries to get through a door, her playstyle involving messing with enemy players' abilities, and an unlockable highlight intro that looks like it's gonna be someone else's PotG, but it's actually hers.