Why is it that my adc doesn't know how to right click on the enemy adc???

Every game against a jinx my adc never tries to kill it and when I question them as to why they aren't focusing the only thing carrying the enemy team they say stupid shit like

"I'm vayne I can't focus jinx"

We are in a teamfight... and you die anyways BECAUSE YOU CAN'T RIGHT CLICK ON THE ENEMY ADC??

/endrant

makes no fucking sense to me