LOL!
"kys" = instant in-game execution by nearest non-player (some sort of global unique death message to both teams indicating this was why he was executed), accompanied by 25-game chat mute. Also, your screen turns gray for the rest of the game, and you appear to everyone else like a Mordekaizer ult ghost.
"I hope your mom gets cancer." "die of cancer" etc = You now passively spawn Teemo shrooms around your champion which only detonate on yourself. Think Zyra seedlings. Except they're shrooms. Hope you're the type to buy pink wards and sweeper....
"ur a 12-yr-old in your mom's basement"= you're now chased by every jungle mob you pass (including scuttle), which has now been transformed into non-smite-able gothic Annie while they're aggroed on you. Wolves is 3 Gothic Annies. You should probably avoid the wraiths. Killing them or their Tibbers yields no gold.
"ur fcking useless," "ur trash" etc = Congrats. You now have
on you the rest of the game.