Don't flame on people in game if they end up getting team countered
if the enemy team is
don't flame your glass canon carry if they dont make it though every team fight
if the enemy team is
don't flame your melee teammates if they don't do boatloads of damage every fight
I could go on but I think I've made my point. just because a champ is strong or meta doesn't mean they perform optimally in every scenario. most champs have an opposite and most players have an opposite mindset that will rock their world. So unless your team sits in an arena with sponsors and cheering fans, don't wail on them for being dealt a bad hand.