One of my favorites comes from the most unlikely person.
: "If at first you do not succeed... please, tell me what it is like."
The second comes from a really good trash-talker.
: "I hear you're trash. Bow before your king!"
And the last comes from the Aladdin of Zaun.
"Seems you left your brave pants at home. Want me to wait while you go get them?"
"It seems your chances of survival are... less than zero."
All of
's taunts tbh, but here's a few:
to 
: "What do cops and donuts have in common? I dunk them!"
to 
: "You'll go where I tell you Mundo."
to 
: "Arrrr... You suck."
to 
: "Hey Lee Sin, feast you eyes on - oh, my bad..."
to 
: "Oh no, it's leona, I'm gonna get a tan."
to 
: "What is it you mastered Yi? Sucking?"
to 
: "I don't get nightmares Nocturne, but you are putting me to sleep."
Oh gosh there are so many good ones I just need to stop here before I overdo it xD
"You belong in a museum!"
Easily the best quote in the game.
Forecast 
"It looks like there's a low chance any skill shots are gonna hit us"
"You will lose."
Don't have to sugarcoat anything. Pure,unadulterated taunt,right to the point.
: "You're as modest as a freshly-paid courtesan" to 
#LookingDownOnThemBJSkillz
Death is not the end for you. I have seen to it. For eternity; YOU. ARE. MINE.
Badass, terrifying, and strangely poetic all at the same time
I have a deficiency....in cares...
"I don't care what your name is!"
"Come, test yourself in the fire!"
"There's no coming back from your demise!"
"I've seen your death, it was painful."
"THE TIME OF MAN HAS COME TO AN END."
I loved Katarina's taunt before they removed it for some unknown reason.
"Killing is my duty, fun is yelling SURPRISE!" <3 I wish they put it back. The ones she has now sounds like she's getting punched in the gut in the middle of her sentence. 
"You're already dead, you just haven't caught up yet."
"You only need to click once, FOOL!"
"If I eat you, will I learn to die?"
One of my favorites is 
's taunt to
"mmm urgot, I highly reccomend Death at this point"
"It's over when I say; oh Yes, it's about to get Much Worse"
"Knock it off, I'm done being Nice"
"Run playthings; I will Not hold back"
"You cannot fathom what I am!"
"There is something sublime about holding a heart in your hand"
"You're seriously asking a Giant demon Bird, for a JOKE?"
"I haven't got a Brain!"
** BEATEN BY A LITTLE GIRL** (The voice actress sells it).
There is only one:
"So many noobs...will matchmaking ever find true balance?" - 
to
So uh, Urgot... we can't hang out any more. I'm cool now.
"For my next trick, I'll make your lifebar disappear,"
"Their tears shall salt the ocean!" --
"How they try!" --
I'll think of more, but in a match right now. That's one of my favorites though.
there is such potential in one mortal life. you have wasted yours.
force is meaningless without skill.
not quite a taunt but quote when you pick him in champ select:
"Call me king. Call me demon. Water forgets the names of the drowned."
and that's some cold shit right there i get chills every time fam
Imagine if I had a REAL weapon.
Why has this not been mentioned. o.0
chimes
"Force is meaningless without skill."
: I won this fight already- doing it again for fun
FUCKING. SAVAGE.
"I suppose you are expecting some unbearable pun"
not sure why but i laugh every time.
is by far the King.
Dunkmaster can be close..
"A legion couldn't stop me, what chance do you have?"
puts enemies on tilt with his amazing laugh coupled with:
"You should come back with more bad guys"
- "COWAAAAARDS~!" (while ulting away from the enemy)
