Jerk lee sin

In pregame lobby my friend hovered kayn and was gonna pick him then accidently swapped to hover jax. So the jungler asked him to pick kayn for him and then my friend picked kayn for top lane. he told the lee sin it wasnt for him and in pregame lobby lee sin said he was gonna int top. i was already tilted so i was a little harsh with my langage but i called him out and he said i made a mistake. so lvl 2 he walks into my lane and feeds my laner a kill standing still. then after that in game i admitted that we lost and since hes inting he won then he flamed me and told me to kill myself and i mean i dont usually get flustered as much over feeders but the whole thing was unfair and i just want an opinion or help on this i have a screenshot of him flaming in case you need it. i cant figure out how to add it though.