Jg item farming penalty... if you are a laner!

Sooo.. today, i queued as adc (definitely not lulu! xd), and the enemy team picked 4 tanks.. -> decided to go for max hp on-hit. You know, .. also, i wanted the red smite buff asap so bought it before completing the item. And, got the minion g reduction, though not trying to become yi.. :((

Rito, how about having a min amount of monsters you need to kill before the penalty kicks in?..