While most of the time, Jojo's Bizarre adventure is a serious battle manga, most of the cast is completely insane. Half the fun is watching them pull out incredibly zany schemes, hurt each other in increasingly ridiculous ways, or play off each other, with their own brands of Insane Troll Logic.
Speedwagon's reaction to Jonathan and Erina sharing a tender moment. "Speedwagon withdraws coolly."
After his Training from Hell, Joesph shows off his new abilities by challenging a mugger to stab him. When he tries to do so, he stops the blade with one finger, and then pulls out a container of mustard and squirts it all over the mugger's head. After about a page or two of suspense, Joesph admits that that last part was just to mess with him.
At the end of the Hell Pillar Climb, Joseph is about to slip off the wall. Caesar grabs his wrist... only to remember that he's exhausted, too. "26 seconds later, after Joseph said 'Don't let go!' thirteen times..."
In the anime, Joseph peeks in on Lisa Lisa while she's bathing. Later, in Lisa Lisa's epilogue, after a mention of her being his mother, he can be seen with an utterly disgusted look on his face.
In part 3, Joseph has to land a jet, when his prior experience had been with propellers.
Joseph: Hey, Jotaro. This'll be my third crash landing. Heh, have you ever known anyone that crashed three times? Beat Jotaro: I will never fly with you again!
Before taking the camel, Joseph suggests crossing the desert by helicopter but Jotaro reluctantly says that he's not flying with a guy (Joseph) who has crashed three times in his life.
And then the incident with Mannish Boy marks the fourth time Joseph crashes a plane. At that time, Jotaro had to fly with his grandfather again. And yes, the plane crashes. Jotaro mutters "I just knew it" as it happens.
Joseph and Avdol's adventure while battling Mariah. Especially when they get into a spot of trouble in the ladies' bathroom.
Avdol: "Disasters in the bathroom" is Polnareff's department!
In Part 3, During Jotaro's poker game Batman Gambit against D'Arby he keeps collected whilst D'Arby steadily goes even more insane. After the game is won, Abdul checks Jotaro's hand finds that rather than having a hand that could beat D'Arby's 4 kings hand, Jotaro had absolute garbage. Cue Abdul and the kid dealer nearly face faulting
Jotaro repeatedly stealing various objects with his Stand while locked in a jail cell in the very start of the arc, somehow managing to snag RC cars, weights, motorcycle helmets and an exercise bike. Some fridge humor comes into play when you realize that Star Platinum is a short range Stand.
When Polnareff runs into a still-living Avdol after he apparently died, he enthusiastically brings him back to the others, only for them to act completely nonchalant about it. They were all in on a plot to fake Avdol's death (with Hol Horse and J. Geil's unintentional help.) and didn't tell poor Polnareff because they feared he had a loose tongue.
In a darkly comical way, the way Dio bluntly told Senator Wilson Phillips (Who Dio was forcing to drive him around Cairo after the escaping Joseph and Kakyoin) that he wasn't going to let him go alive. Dio was so blunt with the poor guy its hard not to laugh.
Polnareff's first experience with an Indian toilet. A pig pokes its head up from the bowl. The bellhop hands Polnareff a stick with which to fend it off. And then the bellhop recommends letting the pig lick Polnareff's butt clean!
Hol Horse and Boingo's team up. When they're in an Egyptian taxi, Hol Horse is about to let Boingo out of the suitcase he was held captive in. Bear in mind, Boingo was on a plane, too AND Bound and Gagged. The very first thing Boingo does when Hol Horse removes his gag? Puke all over him.
Hol Horse: Still a little airsick are we?
Jotaro's reaction when he's called over to remove a mind control parasite from Polnareff. It's one of the few times you see him actually smiling.
On their way out of India, the heroes pick up the runaway girl from earlier, who's hitchhiking. She tries to get Kakyoin's attention by talking about how she'll have to wear a bra soon. The reaction?
Caption box pointing at the heroes: NO ONE CARES
Anubis on being at the bottom of a river: "I'm so lonely!"
Josuke's Hot Mom leaping onto Jotaro, thinking that he's Joseph, hugging him and telling him how much she missed "him." While still amusing, what made it hilarious was how coldly he reacted to having such a cheerful and cute young lady hugging onto him;
Part 4 has it's moments, but the entirety of the arc, "I Am An Alien!", definitely deserves mention.
During the aftermath of Josuke burning down Rohan's house, Rohan keeps his cool.
Josuke: Uh, sorry about yesterday. The fire was, um, pretty bad, right?
Rohan: Yeah. I had a complete replica of the Drexel Heritage furniture used in the movie "Pretty Woman" valued at 2.5 million, which was damaged beyond repair. Not that I care or anything.
Josuke and Okuyasu eating at Trussardi's restaurant. Seriously, the entire thing!
Old Joseph mishearing everything.
Okuyasu: 'Red Hot Chili Peppers'!
Old Joseph: 'Pop pop pop the popper'?
There's something darkly hilarious about Rohan and Josuke laughing with each other during their game, then Rohan slamming a knife into his own hand and cutting his finger off to show he's not fucking around.
Also comedic in a rather dark manner is all the shtick that Kira goes through in order to get back his 'girlfriend'. It almost seems like something from a Three Stooges show. What it leads to however...
A rare one from Kira.
Kira: By the way, do you have a tissue? Or a napkin perhaps?
Koichi: I don't...Why do you ask?
Kira: I see...Well you can use mine.
[Kira punches Koichi in the face]
Kira: Nosebleeds make a big mess, so I thought you might need one.
When Josuke finally catches up to the Stand User who has almost killed him and Rohan in the town's hospital, he finds the villain is a bed ridden invalid, who tries to appeal to Josuke's good nature by asking whether he would really bully a weak and helpless cripple. To this, Josuke responds by healing his injuries with Crazy Diamond, and THEN:
Anytime Anasui tries to get a sweet moment with Jolyne; they're either just happenstance that he interprets as romantic opportunities or absurdly contrived set-ups by the man himself (such as getting FF to trip Jolyne just so she'll fall into his arms;) either way they usually end at his expense.
Jolyne, after regaining her memory, sees she wrote a note to herself that say "Don't forget to wear your panties". Her realization is priceless.
Hermes tries to cheer up Xander.
Hermes: Whenever someone says "Today was a bad day," they'll say to themselves that "Saturday will better." That's how we continue to live! No one lives a life of only Saturdays!
Xander: I was arrested on saturday.
Even funnier: before that, Hermes offered Xander her panties. And he was actually interested, too!
Steel Ball Run
Stephen makes a horrible joke after going into a speech about a large block of ice holding the SBR trophy:
Stephen: Well, I think those comments, broke the ice, don't you think?