People target ban their teamates and then cry when they int?

I don't understand why you'd get mad at someone trolling you after you trolled them? And especially when people ban their teammates Yasuo or another contested champ (and of course I mean when they have declared it) because between autofill and the constant senseless whining about "OP" champs that really aren't there are several champs you will rarely get to play so when its banned by your own team people are obviously going to get mad.