The Emperor talks too much.

Luke was clearly never trained in repartee.  As soon as it was clear Emps was going to monologue, he should have just fired back.

EMPEROR:  monologues about the Dark Side.

LUKE:  Forcedamnit old man, are you fucking trying to talk me to death? Shut up already.

EMPEROR: monologues louder.

LUKE: Seriously, dude, the first "Death Star" (finger quotes) got splattered, just like those drone control ships from the Trade Federation.  You weren't even original, and wasted a shit ton of money.  Is your dick as shriveled as the rest of you?

EMPEROR: monologues about "insignificant rebellion."

LUKE: Yeah?  So why did you bring an entire fleet AND a "Death Star" (more finger quotes)?  It's pretty clear you're scared. And why a second "Death Star"?  The first was Viagra Star and this is Cialis Star?  What's next?   Some sort of planetoid that drains suns or something? How original.

EMPEROR: Angrily monologues about the power of the Dark Side.

Luke:  Are you still blathering?  If it's so damned powerful, why the shriveled face, shriveled dick, reliance on mundane weapons and unoriginal thinking? You don't even have a harem?  It's pretty clear why it's "Dark." It's the opposite of "Bright." 'Look at me! I rule the galaxy!  I have to send entire fleets around to get the shit kicked out of them by wookies, retired Jedi, half-witted smugglers and gamblers and bumpkin farm boys.  I'm ugly, shriveled and don't have a woman. I have a creepy relationship with this orphan I helped mutilate. But trust me, this is as awesome as it gets!' You are one disturbingly pathetic geezer.

EMPEROR: throws ruling the galaxy out there one more time.

Luke: Yeah, you keep on with that. It's like you're Amway or something, multi-level marketing your repression.  'Oh, please! Take over in my downline!  I'm all powerful but need help ruling!' What have you done with the galaxy?  Is GDP up?  What about GINI index?  You're like the eight year old bully who steals all the balls in the neighborhood, but throws like a girl and can't bat even with the balls, in more ways than one. If this is the best the "Dark Side" has, I'm yawning.  Rent yourself one of those blue chicks with the head-handles and get blown. When you can accomplish just that, come back and we'll talk. From here, I see nothing worth my time.  You're old and need a replacement.  I don't need you. Go force choke your chicken.