What if their way of "owning up to playing bad" is to not say anything (because at this point their teammates will probably have flamed them incessantly and been muted anyway) but it was to adjust their playstyle to the situation.
Like for example, say you're an AD top laner like Fiora and you wind up getting completely shit on, like 0/8 or something. You're so far behind that you don't contribute much, even to a 5 v 5.
I'd say at this point, the best strategy is to solo push lanes/split push, probably even use TP to return to lane and not to join team fights and here's why.
- If the enemy team devotes someone to kill you, so what? You're not worth any gold to them at all, and it creates a 4 v 4 for the rest of your team, AKA a fair situation instead of an unbalanced one where it's a 5 v 5 but you're so behind that's it's really a 4 v 5 even with you there.
- As an AD champ, you can actually take objectives fairly quickly if left alone. This could make up for your bad game putting your team in a 4 v 5 if the enemy team doesn't devote resources to you and groups instead.
- If you realize you're useless in a teamfight, TP can be used to gain strategic advantages. Say you go into a lane by yourself and get killed....again....well if TP is up, you can just go right back there and finish pushing lane/taking that tower. You've bought time for your team, and a possible way to win later. There's also the last ditch solo nexus kill, should that opportunity present itself.
- Since you're probably losing to the most fed person on their team, who will probably peel off to 1 v 1 you, it won't take their whole team to kill you, meaning you can take advantage of this and not give up assist gold like you would be if you died to that same person in a team fight.
That's just a few thoughts, granted, not going 0/8 is ideal, but lemons, lemonade etc. I'd rather have someone atone for a bad game by being as annoying to the enemy team as they can, and in this specific situation that's one way to do it, as opposed to simply being present for 5 v 5s in which you'll get insta-deleted. I've spectated games where a situation very similar to this has happened, and one I can remember the team with the player who's K/D/A looked like someone was seriously intentionally feeding actually won, because they did this. Sure they had a bad game, but the enemy team was too stupid to deal with the macro gameplay this created. You can have a bad game and be useless, or you can have a bad game and still win, if you and your teammates realize how you can still be useful when you literally can't win a fight.
Just saying, I'd feel better if the "bad player" did this rather than just say "I'm having a bad game, sorry guys."