This one comes from the g2 comics, Megatron in "Total War"

"Why? That's what they all asked me. Why him... why Starscream? Why, of all the Decepticons, did I decide to revitalize the one whose record of deceit and betrayal is legend? Because I'm an idiot, that's why!"

Always makes me laugh

 

Quintesson Judge: Silence! Or we will hold you in contempt of this court.
Hot Rod: I have nothing but contempt for this court!

 

Nearly forgot Rotorstrom's epic line from Last Stand of the Wreckers: "Wreckers, combine!"

 

When Optimus Prime said "Boobies"

Oh, you wanted the full quote? From the G1 episode "Prime Target":
"Amazing, a booby trap that actually captures boobies."

 

"Are you damaged?"

"Just enough to make me interesting"

 

Prime's speech in TF1 at the observatory.

Springer - "I got better things to do tonight than die!"

A lot of BW Megatron's dialogue was great. But I have to go with "Oh, Whatever!"

 

The problem with text quotes? Never sound as cool as they actually are.

 

Unicron in TFTM

"Your bagining posture is highly dubious, but very well. I shall provide you with a new body, and new troops to command."

Megatron "AND"

U "AND NOTHING! You belong to me ,now."

M "I belong to NOBODY!"

U "Very well, then proceed on your way to oblivion!"

 

BM Jetstorm:

"This is Captain Jetstorm speaking. Please feel free to move about the tarmac, and flee for your miserable little life!"

Blackarachnia and Waspinator:

"You mean I risked everything to save this... this.. this... scrap heap?! Eww!"
"That mean spider-bot not go steady with Waspinator?"

Obsidian:

"Although he took his name from a great leader, Optimus Primal never learned the first rule of warfare: never underestimate your opponent."

 

Also forgot this one:

 

"I can't deal with that right now."

"I have summoned you here for a purpose."

"Laserbeak returns, Megatron."

"I will rip out your optics!"

 

"In severity lies the strength to know what must be done in order to attain success, and to do so without question or hesitation, no matter what the price to oneself or others. Severity is determination in its purest form. Severity is the shortest line between aspiration and power."
—Beast Era Megatron, "Singularity Ablyss"

"Mercy. How quaint. I see no victories sired in the niceties of mercy. Mercy is the maxim of the weak, the final plea in a victim's eyes, the final gasps in their dying breaths."
—Beast Era Megatron, "Singularity Ablyss"

"Splendor, to me, is perfect order. Programs designed with such finesse that no subroutine contains a single byte of extraneous code. Splendor is a billion soldiers storming a planet as a single unit. Splendor is a mountain comprised of fallen foes. Splendor is power."
—Beast Era Megatron, "Singularity Ablyss"

"And in an instant that lasts a thousands eons, I learn that there is indeed something more satisfying than the howl of a dying beast: the death scream of an angel."
—Beast Era Megatron, "Singularity Ablyss"

"But it matters not; soon the sparks will once again be mine. And when I reacquire them, rather than merely devouring their energies, I will merge their very souls under me. We will become one, with myself as the dominant entity. With all the sparks subsumed under my will, I will return to the Allspark, not as a supplicant pleading re-integration and the relinquishment of my individuality. When next I ascend this Tree of Life, I shall assimilate the Allspark under me! I was a general, a leader of troops. I was a king, reigning over a planet. Why did I ever trouble myself over such ridiculous minutiae? Soon, so very soon, I shall be a god. Yessssss."
—Beast Era Megatron, "Singularity Ablyss"

"The end is near Optimus Primal... yessssss."
—Beast Era Megatron

 

So many. Prime: One shall stand one shall fall! T'ill all are one. Starscream: I live to serve you megatron. Soundwave: As you command megatron. Eject! Eject!! EJECT!!! Megatron: I'll rip out your optics!!!

 

Grimlock: Me Grimlock like big fight!

Rodimus: Good, 'cause you Grimlock have got one!

 

Noone calls me a robot chicken - Brawn

 

Starscream: It looks like some kind of... rust!
Megatron: Impossible! We are rust-proof!
Starscream: Perhaps you're made of shoddy materials, Megatron!
Megatron: That's ABSURD!