Jack's attempts to get a job to prove Crow that he could. He ended up being a chef, working in a book store, and working at a dry cleaning shop, only to get fired from all three jobs in a relatively short amount of time.
Jack arguing with Leo over who's better, him or Yusei, in episode 43.
Saver's reaction to seeing Carly after blasting her out of his window.
Saver(To Himself) "Ok, you're having a nervous breakdown, it's the stress of your job, it's gotten to you, I hope."
"I'll avenge my cup ramen!!"
When Jack's three potential love interests try to visit him in the infirmary:
Mikage: Let me in, I'm a cop!
Carly: I've got a press pass!
Stephanie: Ummm... Here's a coupon for coffee!
When Martha teases Yuusei about his relationship with Aki.
Pretty much anything Jack does in episode 115 is hilarious including jumping 8 feet into the air to get to an arcade machine and getting beaten by Cup Ramen Man.
Episode 132 gives a CMOF to Jose, of all people, when Placido returns to the pit at the end of his duel with Jack. Jose mounts his D-Wheel, which had been in hiding up to this point, by running at it, leading many a viewer to believe for a moment that he actually planned to race against Jack on foot! See it here at 4:15.
Crow's expression when he sees how much one blue eyes mountain coffee costs - 30 dollars for a cup of coffee!?
Episode 138 - Yusei and Team Ragnarok put together a plan to get to the Ark Cradle, involving Bruno and Old Momentum. Seeing as the Rune Eyes and Yusei's Birthmark can power their D-Wheels, Bruno rides an ice cream cart to get there, towed by Team Ragnarok's D-Wheels. Brave's entrance with it to begin with was hilarious.
The Japanese version has Crow memorably shout "Oh my God!" in English, followed by an indecipherable Popeye-esque rant during a duel. The contents of the speech go something like, "Yusei, I'm sorry, I really am useless against the Dark Signers," until Jaeger tells him to shut up. Jaeger casually muttering to himself about his plan while Crow cries and rants is equally funny, though.
There's a scene early on in the anime, where Yusei was just released from prison and he enters a Bad-Guy Bar because Himuro told him to meet up with someone there. He just walks in like a bad guy, gets up to the bar like a bad guy, and even SITS like a bad guy (elbows on the table and hunched over.) The Barkeep says that kids aren't allowed here, and what does Yusei say? "Get me Milk." note Kid's been watching too much Chuck Norris.
Everything during the first part of episode 114. From the Rastafarian Jaegar, to Jack's reaction when his favorite cup ramen is sold out, to Jack's ridiculous plan and how much Crow suffered during that plan. Really, it needs to be seen to be believed.
Episode 115 is, probably, the funniest episode ever. We start with everyone interrogating Jaeger about the relationship between the Public Security Maintenance Bureau and Yliaster, the show's Nebulous Evil Organisation. He then starts narrating an equally ridiculous and Tear Jerking story about the first time he ate cup ramen with his poor circus family, and how much he liked it, complete with Ocular Gushers. Three times funnier because of Jack crying as much as him, saying he understands his love of ramen, and giving him several boxes of ramen as a present. Then Sherry gets pissed and tells him to get to the main point. He agrees... only to continue with the story about how he joined the Public Security Maintenance Bureau to be able to provide ramen to his family forever.
Episode 14 has It a random street duelist that sounds suspiciously like Joey Wheeler. "Nah, it's his cousin, Jesse Wheeler."
Episode 99, Jack's fangirls have to get past a security guard to see him. One has a police badge and one has a press pass, so they can get through without a problem. The third is a waitress, so all she has to offer is a coupon for a free coffee. The guard is so flabbergasted it actually works.
Sly's filler episode intro. Ruka and Rua drag along Sly and their usual friends to Yusei's workshop where Yusei, Jack and Crow are working on Yusei's D-wheel. Then this exchange occurs (paraphrased for lack of memory).
Ruka: You should really see this, Sly. Yusei's D-wheel is really awesome.
Rua: Yeah, but the last time we came here the engine exploded.
Yusei: *completely Deadpan* Don't worry, you won't have to worry about the engine exploding...
*cue the Auto-shuffle for his D-wheel malfunctioning and spraying cards everywhere from behind Yusei, who doesn't move as it occurs*
In Episode 14, Yusei's working on his duel runner, listing to the theme song (which is apparently a band in New Domino City or something), when Tanner, Blister, and Yanagi walk in. Before they even say anything, they instantly cringe at the music and exclaim to turn it off.
Jack: If they try to take us on, I'll give them a barrel full of Jack Attack.
DUB Episode 6 has a gem as well, also from Jack, after Rex comes with the first of many explanations about what Yliaster is. Too bad his explanation is later proven to not at all be true.
Rex: The Yliaster is simply the force that keeps the entire universe together.
Jack: So it's glue. You swore an allegiance to magic glue!?
Also the scenes after his first turbo duel. He grabs a microphone from a reporter and starts informing the crowd that he can beat anyone on any runner. He then loudly proclaims himself the "master of faster" and the "ruler of the duels".
Mikage: Um, Jack, I have to disclose something. I think I might have special feelings for you.
Jack: 'Course you do. But we're talking about Carly right now!
Considering the Jack/Mikage/Carly love triangle, Carly would've laughed her butt off if she heard Jack say that to Mikage's face!
From DUB Episode 38, when Sayer sees Carly after he had "killed" her previously he says to himself
Sayer: Ohhhkayy... you're having a nervous breakdown, it's the stress of your job, it's gotten to you... I hope.
These lines from Lester (or Luciano in the original)
Lester: Good one [Jack], you're as funny as you look.
Lester(talking to Primo after purposely losing to Jack): You're the one who would have lost if I had been the one to win at rock paper scissors. (pause) Stupid scissors.
(the idea of Primo/Placiado playing rock paper scissors is pretty funny too)
Carly hiding among Jack's gifts in the final episode.
Jack being completely deadpan with his arms crossed on all the rides at a theme park while Carly, Trudge, and Mina are screaming their heads off. Even on a bungee jump.
Carly's rant to her Jack hallucinations in Episode 37. In desperation, she tells them she wants to take everything she did for him back, and the fact that the things she mentions differ between Japanese and English versions makes for twice the funny. The last thing is either embarrassment for having to wash his men's clothes or her flirty looks. And her ending line: "And I want my heart back. I want it to not be so broken." Yet the scene shows just how overwhelmed she is with having her heart broken, so it's more Narm Charm than anything.
Episode 68 in general. Crow is tricked by the kids into doing something, while Jack and Yusei give each other a Are-You-Joking-Look.
The faces Aporia make in Episode 143 are utterly hillarious, especially one the right after jack destroys the last of his permanent cards.