The fact that the ghosts had no idea what to do with Danny after they finally caught him in Strength In Numbers
Sam training to control her fire powers was pretty funny, especially when she accidentally set Dora Mattingly on fire.
Jack and Maddie being inside a tornado in Hearts and Minds and not even realize it.
"We must've passed that same house three times now".
In the same story, Danny and Sam (who don't remember each other) come face to face with Nocturne.
Both: NOCTURNE?! How do you know Nocturne?
Danny: Okay, that was weird.
Then again, when Tucker appeared.
Both: TUCKER?! You know Tucker?! Grr. Stop doing that!
In A Family Thing, after a ghost battle left Danny and Sam messy, Jack attempted to clean them up with the Ghost Weasel, only to accidentally suck them up. Sam's comment following it was just the icing on the cake.
There was also Jack's Running Gag of accidentally shooting someone with the Fenton Foamer.
Jack causing half the city to blackout in Stolen Years, complete with an angry mob appearing on the Fentonworks front step, lead by Sam's parents.
In Junior Hijinks, when the Groovy Gang encounters Danielle, Scaredy Cat runs off, dragging his two companions by the leash back to their van, hops in the driver seat and speeds off to parts unknown.
Danielle: "Today I learned that tigers can drive vans."
Then later, after Danielle deals with the Extreme Ghost Breakers:
Medic 1: Uuuh-hhhh, not these nuts again.
Medic 2: (Pointing to Sullivan) Quick, let's just get that one in the back and sedated before he goes and says...
Tucker and Valerie encountering SkulkTech in City Hall's underground bunker in Pairing Off. Technus said it best.
Technus: Well, uh, this is awkward.
As well as this line from earlier when Skulker and Technus find themselves stuck together.
"Perhaps your limited intellect is incapable of grasping even a concept THIS simple, but if I KNEW how to split myself away from this primitive smattering of refuse you so amateurishly refer to as technology…DON'T YOU THINK I WOULD HAVE DONE IT ALREADY?!?!?!"
The Fentons and Tucker trying to keep Little Danny and Little Sam from tearing apart the house in Stolen Years.
While fighting Desiree, the wishing ghost uses her powers to zap Danny and Sam into a 4-H lot, feeding animals. After she takes off, Danny follows, only to find Sam stayed behind to finish feeding them.
Earlier, when Valerie, Jazz, and Tucker came to their aid, the three of them clumsily tried to stay on Valerie's jet sled.
When Tucker's robot first appeared, it scared Dash silly because he thought there was an invasion. As if that wasn't enough, when he found out Tucker was the reason, he got so mad he actually ran up and punched the robot, thinking Tucker was inside it. The result of him hurting his fist and jumping around howling in pain was so hilarious even Danny, Sam, and Tucker couldn't keep their composure.
Box Ghost wearing Danny's clothes in Bad Breakup.
In the first story of the series, Jack attempted to fire his new Ecto-Bondo weapon at Future Danny, only for it to miss and destroy the lab before trapping Jack, Maddie and Jazz. It was so funny, even Future Danny couldn't keep from laughing.
Clockwork calling Vlad a fruit loop in the first story of the series.
Sidney and Desire's new jobs at the end of What She Wants will have you howling and feeling fuzzy at the same time.
At the end of the first story, when the Fenton RV arrives with Jack, Maddie, and Jazz:
Maddie: Next time our son is facing a life-or-death crisis, I'M DRIVING!
Jack: I still don't see what the problem was! The sign said it was a one way street. We were only going one way!
Jazz: Well, that's very logical Dad, but did you happen to notice how all the other cars were going in the opposite direction?!
In Laws of Attraction, we have two of Walker's guards that were unfortunate enough to be guarding Paulina:
First guard: "Unnh…That's it! I'm putting in a request to get this brat in suspended animation!"
Second guard: (With his hands over his ears)What?!
In Ancient History, Danielle's reason for her appearance after Amity Park is transformed by the Scarab Scepter.
I was just eating in the lunch room, totally minding my own business, when my sandwich...my delicious peanut butter and blueberry jam SAND-wich...turned into...wait for it...SAND! SOMEONE around here owes me an explanation...not to mention LUNCH."
In the same story, we have a Running Gag of Sam setting Hotep-Ra on fire, him regenerating and shouting his Catch Phrase "I...AM...RISEN!", only to be set on fire again.
Hotep-Ra: (After being set on fire for the third time) "OH COME NOW, THAT'S QUITE ENOUGH!"
Danielle using Wulf as her trick or treating back up, much to Jazz's dismay.
The ending of Hearts and Minds. You'd have to see it for yourself.
During a scene where someone was spying on Danny and Sam having a moment, we get this line from Sam:
"Hey! Unless you want that door to become a permanent part of your face, I suggest you keep YOUR PEEKING EYES TO YOURSELF!"