I'm getting cancer watching the lee sins in my elo. I lost the last 2 games because of a lee sin lmfao. And my win streak was against lee sins. Some are really good at snowballing, but most of these guys think that if you land a Q you have to ride or die no matter the situation. I don't get it.
And even among these who are good at snowballing, half of them are also good at throwing and blaming team.
Best thing you can do is be the jungler yourself so you can ensure your team doesn't have him, then collect freelo off the enemy team's Lee Sin.
Lee isn't the worst person to have on your team though - when I see him I usually have at least some hope of a won game. It's LeBlanc that I fear - in 43 ranked games this season (all in Silver), I've yet to see a LeBlanc win unless she's been carried hard by her teammates. It's got to the point where I very heavily consider dodging if my mid locks in LeBlanc because I cannot remember the last time a LeBlanc on my team didn't lose lane extremely hard, even when paired against champions she should counter. I don't know what the problem with Silver LeBlancs is but they just seem completely incapable of doing anything useful.
I dread most flashy champions and assassins being picked on my teams because nobody actually seems good at them and champions like Zed and Fizz I typically expect to need carrying, but LeBlanc is the worst. It's hilarious that people in low ELO will complain about her being OP when so many of them have so soundly proven that it's hard to do well on her.
I play Diana
and had to learn the hard way not to press R after landing my Q. Especially against Heimer.. 
It's the same problem for Lee... the trigger finger syndrome..
You don't even have to be good at Lee to carry with him in Silver.
