Mxy: Your three months are up. And this time, you're not gonna cheat me out of my fun!
Clark: Oh, it's you again, Mr. Kltpzyxm.
Mxy:Not "Kltpzyxm!" Mxyzptlk! Now, the first thing I'm gonna do- Aw, nuts. *poof*
He builds Powered Armor (complete with pants zipper!), goes to fight Superman, and doesn't last three seconds. Whatever happened is a Noodle Incident, but his reaction after the defeat just sells it.
His counterpart, Gsptlsnz, sells it perfectly the moment he leaves.
Mxy: *disappears with Powered Armor* Gsp:5...4...3... Mxy: *reappears* NUTS! NUTS! NUUUTS!!! *points at his wife* NOT. ONE. WORD.
And of course we cant forgot Ol' Myxie getting stranded on Earth for three months in his second appearance as punishment for his repeated torment of "lesser lifeforms" in the third dimension, and told that he'll get his powers back in three months if he's shown that he can perform good deeds for said lifeforms instead. Cue Superman putting Myxie in charge of keeping a look on Bizarro on the alien planet he left him on, complete with being forced to put his fake city together so Bizarro will have a place to "protect" and getting mauled by Bizarro's vicious alien "dog".
What really sells it is the fact that Superman is watching the whole thing from the Fortress of Solitude with the biggest, smuggest, most self-satisfied grin this side of Superdickery.
Superman: Life am good.
In World's Finest:
Joker: *abruptly busts in on a room full of gangsters* Caesar Carlini, my old pal! Why, I haven't seen you since... *pauses, thinking hard* Waaait. I've never seen you, have I? Wow, you need to get out more.
Especially with the fight beginning with Mercy doing a Dynamic Entry.
When Superman shows up to stop him from interrogating a thug, Batman grabs his arm and throws him across the room. The look of utter shock on Superman's face is fantastic.
Superman: You've got your information, now—.
Batman: [grab, judo throw (letting go of the thug he was interrogating)]
Batman: [notices thug running away, starts pursuit... only to be shoulder-slammed so hard by Supes that he crashes into the far wall]
Superman: I heard you were crazy. I didn't think you were stupid.
"Hello Mr. J. I'm Batman. Eat me. Eat me. Eat me."
Another priceless moment is after this confrontation when Superman goes back to his apartment and undresses for bed while having a conversation with Lois. He notices something glowing on his cape and finds that it's one of Batman tracers. He looks outside his window to see Batman watching him from several rooftops away, which means Batman now knows his secret identity AND where he lives. Batman tops off this awesome moment by saluting Superman before he leaves. Bad. Ass.
Lois Lane has fallen hard for Bruce Wayne, then finds out he's Batman. She is less than happy.
Lois: I'll get some iodine for that cut. (through clenched teeth) Burning. Stinging. Iodine.
The cherry on top is the look on Bruce's face when she goes to get said iodine: pure bedroom eyes mixed with amusement at her comment. Oh, Bruce. You dog.
The scene begins with this exchange - the douchey yet teasing way Bruce delivers the line is what sells it.
Even better-when Lobo goes onto a "kid-friendly" for tv-swearing little rant fest...as Superman sent him flying-the hole that was ALREADY in Lex's office from Lobo and Superman's fight, you see a very ticked off Lex Luthor, ordering his goons to....
Luthor: *ticked off* but I want all repairs completed—
*cue Lobo being thrown through Lex's office again—this time from the floor straight through to the ceiling* killrendfragdestroy—!
Luthor: *even more ticked off* IMMEDIATELY!!
Pretty much everything that comes out of Lobo's mouth is hilarious, but the following is particularly funny in its delivery:
A subtle one, but when Lobo arrives in Metropolis, he makes the rather sensible decision to just ask where Superman is by walking into a police station and showing them his picture. Even better, the desk Sergeant barely bats an eye at the hulking white-skinned red-eyed guy who shows him a holographic three-dimensional image of Superman.... he just explains calmly that the police don't keep tabs on Supes. That either speaks highly of the professionalism of the Metropolis PD, or it's just that they see weirder stuff than Lobo on a routine basis. Then there's the way the conversation ends....
Cop: [Superman] only shows up when there's trouble.
Lobo: I can do trouble..... *racks gun*
Throughout all of Part 2, whenever Lobo winds up facing some sort of opposition trying to stop him he simply replies "Who's gonna make me?" only for said opposition to start smacking him around. When this happens near the end when he's confronted by the Preserver, the Preserver proceeds to transform into a red behemoth. Lobo realizes he may be just a bit Genre Blind...
Lobo: You know, I really gotta stop saying that!
In "Knight Time", the reaction of Bane as Superman, dressed as Batman, beats the crap out of him with his bare hands. The look on his face is just clearly going, "Oh bullshit!"
Robin: (to Riddler) He's been working out.
The "That's it, no mister nice guy" look Supes aims at Bane before applying the beat-down.
Then after that, screwing with the Mad Hatter using Super Speed. The "Oh Crap" expression does not leave the Hatter's face once in that entire sequence.
Mad Hatter: Curiouser and curiouser!
And when Superman forgets himself and grins at Robin. It totally freaks out the Mad Hatter until he remembers he's playing Batman and scowls again.
Similarly, as Superman emerges from a fireball, his Batman costume burnt away:
Brainiac: Kal-El. This development was highly improbable.
Superman's deadpan reply is also gold.
Superman: Today's been full of surprises. *punches Brainiac*
Also in "Knight Time", when Tim Drake (Robin) asks Superman how he can imitate Batman's voice so well:
Superman: (doing Robin's voice) Plus, I have a pretty good ear.
Robin: (turns and glares at Superman) Don't. Do. That. Again!
Really, seeing the Boy Scout pretend to be Batman was hilarious.
Not to mention, it's a fun Lampshade Hanging on the limited amount of character models available at the time that Superman can pass himself off as Batman (who at least in the comics is quite a bit thinner).
That depends a lot on the artist, some versions have Batman being even more muscular than Superman, while in others, he's got more of a martial artist build.
In "Warrior Queen", the whole sequence of Superman fighting Maxima is witnessed upon by an older woman. Her comments to her husband about everything going on, and her husband's responses to them...HILARIOUS!
Wife: Murray, there's a man and a woman fighting!! Husband:[not taking his eyes off the newspaper] Stop spying on the neighbors, Lucille.
When Maxina hugged Superman for actually beating her.
Lucille: Oh my goodness...now they're hugging. Murray: Don't get any ideas!
Heck the reaction of Superman when Maxima expresses her joy that Superman beat her!
Maxima: No one has lasted this long with me - no one! You are...my equal!
(Maxima abruptly hugs Superman)
Maxima: This is the happiest day of my life!
Superman: (dumbfounded) I'm...glad?
After Superman explains to Maxina about Earth's concept of love and marriage.
Lucille: What planet is he from?
Plus, the out of nowhere cameo of Lobo. Naturally, it's love at first sight.
If we count the redubbed Kids' WB! promo spots, I nominate this one using footage from the episode where Superman raced Flash:
Best part, in the beginning of the next episode....SHE DOES!
This bit from "Superman's Pal": So you know how stupid mooks always try but fail, every time... to shoot the Man Of Steel? Some villain tries to hit him with a bar. Superman naturally lampshades this, "You're kidding, right?"
From Bizarro's intro episode:
Bizarro: Me am Superman! Me am hero!
Lex Luthor: Sorry my friend, but you am toast.
Also, Mercy's sarcastic reply when Bizarro asks who he is:
Bizarro: What...am me?
Mercy: "Bizarro", that's what you am.
After Mercy's reply makes Bizarro angry and he flies off crashing through the roof.
Luthor:(to Mercy) That's coming out of your pay.
Not to mention Bizarro attempting to prove he is Superman by "saving" an abandoned building from a wrecking ball and "fixing" a lifted drawbridge just as a boat is about to pass through it.
After Bizarro throws away the wrecking ball crane, it's about to land on a wedding. Superman had only seen the crane fly through the air and not who threw it. After saving the people he simply says, "Don't ask me. I just catch 'em."
Lois: (looking at a picture of Superman) Nice "S".
Clark: Excuse me?!
Lois: Right here (Points to Superman's S-Shield)
Any time Granny Goodness speaks, thanks to being voiced by Ed Asner. Whoever made that casting choice is an insane genius.
In "My Girl" Lana Lang is getting ready to return to Smallville:
Clark: I know you'll find that special person someday.
Lana: So will you; you deserve it. Someone quiet, understanding, patient—
Lois: (From offscreen) Hey Smallville! Get your tail in here; Perry's got an assignment for us!
In "Monkey Fun", one of the escaped monkeys starts jumping on a little kid. His mother tries to get him off, but another monkey starts crawling on her.
Boy: Monkey, monkey, monkey!
Then the boy waves at Superman as he flies away. The monkey waves too.
Superman: I'm sorry Lois, but your monkey friend is going down. Lois: Don't hurt him, he's just a baby! (Jimmy looks at her) Okay, a really big baby.
When Titano is rampaging around the docks, Bibbo, because he's either really stupid or has giant balls (probably both), climbs on top of a stack of crates, slaps Titano with a newspaper, and call him a bad monkey. Titano casually picks him and throws him into a trash barge.