If a teammate does poorly in lane...
...Please don't flame them, and don't act like they're useless the rest of the game. To explain this further, here are two games I had earlier today.
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2217246452/44880503?tab=overview
http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2217231726/44880503?tab=overview
The Nautilus game, the first one, I went something like 0/6/4 to start off with. The Poppy game, 1/6/1.
I showed my appreciation for teammates taking down global gold bounties, and for helping me in my lane (jungler ganks, thank you for those)
I had a good amount of trouble in lane, to the point of being called a feeder if one were so toxic, but because I was not flamed, I was able to get a few items and put myself back into the game (since I wasn't de-motivated by toxicity.) A rough early game isn't the end, it all depends on how they're trying to improve.