Hearthpwn

Quote from Joshbuckler >>

I don't mind a well played or a threaten or whatever when they land the last hit, as long as they do it promptly enough and haven't been roping/emoting constantly throughout the game.

The one that tends to annoy me is "thanks" after you've conceded. 

....it's hard to read intent, though. 

Like I read that as "thank you for playing badly." And I'd hit "Well played" in that situation, much like how you'd shake your opponent's hand after a game of chess. 

But I suppose it would be equally valid to read it as "thank you for giving me a win" and "well played" as sarcastic. Obviously you haven't played well enough when you're hitting concede, after all. 

That said, the exchanges I've had with people who add me as friends tend to suggest that the more pessimistic interpretation is the correct one. 

Yeah the problem is more that the voice acting (for some characters at least) really comes over as sarcastic. 
Like Anduin's "Wow!" or Jaina's "Amazing!", etc
It may not be the player's intent, but I definitely think the character voices are rage-inducing at times, lol

What is slightly more clear as BM, is a "Whoops!" or a "That was a mistake!" after you concede, for example. 

Quote from Joshbuckler >>

 

Emote then concede when you've definitely lost isn't BM. 

 Totally agreed. On the flip side, emoting sarcastically before you play lethal to win the game is hugely BM (in my personal opinion).