I disagree generally with reporting peeps for playing badly, especially after playing a 1st time chen (worst Chen ever played, seriously, I broke all sorts of records that night, ask InSanity) in Single Draft mode (all the heroes were heroes I'd never played, Chen being the only support). Now, don't get me wrong, I'm a reasonably good support (my primary role in most games), but that game was purely horrible and I was probably (scratch the probability, there's no doubt

) the reason we lost that game. Now, I have a 53.26% win rate (196 wins vs 172 losses), which would mean that I'm somewhat experienced.
So how does a player with some level of experience fail that badly regardless of the fact that he or she's playing a hero for the 1st time?
Sometimes people need to remember, that the mindset of the lowest common denominator in the team (the weakest link) in a game that's not going as hoped, differs from the rest of team (no matter how experienced, because I've seen some things that would get a person flamed in pubs happening in top tier competitive games). The rest of the team knows that they're losing because player A is playing a terribly but they'll still try their best to salvage a game, but said player A's analysis of the game, and by proxy their gameplay is impaired because they know that they're the weak link, and as you all know, Dota is one game that punishes mistakes that are made (if you're playing a good team anyway

).
Now imagine all that going through Player A's mind; you're the weakest link in the game, you're probably the reason your team is losing, every mistake you're making is compounding the effect of the previous 2 thoughts. Strain on top of strain (at least in my delightful Chen experience).
Now, you obviously can't play a record breaking Chen without being praised for it, can you (yes, that's sarcasm

)? I had one guy who eventually tuned the hell out of me, even if I apologized earlier and repeatedly explained my hero selection predicament. And don't get me wrong, I'm not saying each player who has a horrible game has the same experience (in terms of situations) as I did, but their reason for playing a bad game can vary and you can never truly know if they're valid or not (who is qualified to say what is a reason valid or not?). I've even had a few horrible Jakiro games (my favorite hero), even one where a guy was like I should never play that hero ever again.
I almost never report for playing horribly (I even tune my clan mates sometimes for doing so), unless you admit to intentional feeding (a few guys have actually done that).
TL;DR I only ever report peeps for abusive language, being jerks, and general bad attitude.
---------------------------------