In a similar vein to most, if not all, of Cartoon Network's original programming (with Ed, Edd n Eddy, Cow and Chicken, Johnny Bravo, and, Time Squad as the biggest offenders), this show sneaked stuff past the censors all the time. However, Billy and Mandy just might singlehandedly be the most blatantly obvious "children-friendly" trope codifier on the whole Western Animation page. The first season is a series of dark and violent shorts that Cartoon Network's censors (if any of them did anything remotely resembling a good job at monitoring content) wouldn't allow these days that begin with the fact that two children befriend Death itself. After this angle was dropped, the show kept its edgy status by delivering at least one stealthy sex joke per episode. Not that the episodes still weren't still full of Nightmare Fuel and Black Comedy; it was there, but toned down. Here's some examples:
The episode "Hill Billy" has Billy visiting Uncle Chokey the chicken juggler.
In "Here Thar Be Dwarves", Billy is cut off reading writing off a wall that says "For a good time call—".
In a very similar case, Professor Toadblatt mentions that someone from Weaselthorph House drew his picture on the restroom wall and added a "For a good time call..." message on it.
In one episode, Billy accuses Grim, among other things, of "watching Mom and dad's 'special' DVD."
In earlier episodes of the show, Grim watches TV programs with some barely audible but still somewhat dirty dialogue, such as:
Actress: Doctor, I'm pregnant! Doctor: That's the third time this week!note Whether it's the woman's third time being pregnant this week or the third time she's told him this week does nothing to change the fact that it's a dubious line in a children's cartoon
In one episode, Billy and Mandy find out that Irwin's mother is a mummy (as in, the Egyptian, wrapped-in-bandages kind), leading to this exchange:
Dick: Yes, Irwin's mom is actually a mummy. Nobody can tell you who to fall in love with, but we've managed to make it work all these years. Leaving a whole lot of questions that don't need to be answered.
Grim: Eh, works for me.
Mandy: Me too.
Billy: ...Yeeeeeaaah, but how did you and Irwin's mom...
Dick:(in the exact same tone of voice) Leaving a whole lot of questions that don't need to be answered.
From the same episode, Billy uses dog crap as shampoo. He says it tastes good.
Grim: Billy, that's not really shampoo. It's dog-
Mandy: Steak sauce.
Billy: Dog STEAK SAUCE? No wonder it tasted so GOOD!!
And then during the credits:
Billy: WAIT A SEC!! This isn't steak sauce! IT'S DOG- *credits end*
There is a answer for how Irwin's dad's relationship with the mummy worked, Irwin's father is Dracula which makes him a Dhampyr and since it makes him a half-monster and mummies are monsters then that explains the compatibility, of course we don't know this until "Dracula Must Die!" Upon putting two and two together this kinda decreases the crap that passed the radar.
"Honey! I have great news!" "You got the surgery!?"
In "Short Tall Tales" we get this: ""You set things right this very instant, or "I'll sue you so hard, your bank account won't know its fees from its assets!"
From that same episode: "This ain't fair, yo! That thing's on 'ROIDS!"
One of the early episodes featured a swimsuit commercial for Speedos. Although it lasted only a few seconds... whatafewsecondsthosewere...
In the Shnissugah episode, how could someone forget it? When Grim tries to access the site, and commits a typo, it's made clear which site it went to... He even tries to conceal the page from the kids!
Another episode has Billy fail to recognize his de-aged mother, where he claims "My mother is ancient and grappling with the onset of menopause."
It didn't help that she told Billy to go to his room when he said that.
When Grim starts dating a goth girl, she asks, "So how do you know when someone's faking it?" and he suggestively says, "Trust me. I know," which prompts the girl to fake a painful screaming death a lathe "fake orgasm" scene from When Harry Met Sally.
Wishbones. It's pretty violent and filled with Family-Unfriendly Death such as an infamous scene in which Pud'n' wishes for a bunny. The segment ends with a bunny, with half of its body blown off, approaching an innocent little kid to probably kill him. Or the one where Skarr asphyxiates in the middle of space.
When Billy asks his father why he shaves, his father answers, ''When Daddy shaves his face, Mommy shaves her legs."
In "The Problem with Billy," Billy's father recollects of an "academic decathlon" Billy and Irwin did as toddlers. When the fathers meet, Billy's dad greets Irwin's with "Hi Dick!" to which he responds "Hi Harry!"
This exchange from the episode Terror of the Black Knight:
Irwin: Good morning, Lady Mandy and... (snickers) Lady Grim.
"Ahoy, matey! Do you want to be a chocolate sailor?"
In "Everything Breaks", Billy breaks his umbilical cord while he's still in his mom's womb. That's a combination of Squick and Nightmare Fuel cranked Up to Eleven.
Toadblatt drank a love potion in "Bummer of Love", and he instantaneously fell in love with Squidhat, a singing male squid, and they proceeded to make out and get married. It should be noted that the Squidhat didn't drink any love potions.
In 'Keeper Of The Reaper' when Jeff is called to the stand, the judge asks him what his relationship is with Billy, to which Jeff replies, "He's my dad!" Everyone in the courtroom voices their disgust until Grim says, "He just hatched the egg, that's all!" and everyone sighs in relief.
When Billy is dancing to a song sung by a brain-shaped meteor he's seen dressed like a pimp.
That's actually a zoot suit (which, of course, is what the pimp suit was based on), much like the ones worn by anthropomorphic wolves in 1940s cartoons (to show that they're playboys looking to get laid) and, of course, The Mask (from the comic book, movie, and cartoon of the same name).
The narrator in 'Dream Mutt': "Now that's what I call doggy style!"
In the Mars episode when Mandy is about to fall from a platform Irwin says "I'll save you Mandy, grab my hand" and Mandy replies "Ew, no way, I know where that hand's been!"
One episode has Grim taking off his robe at a playground and shouting "Look at my body!" repeatedly at several children. It Makes Sense in Context.
From the same episode, Grim starts rooting through Billy's room and finds a bra lying around.
Billy: "Okay I can explain that!"
There's also the instance where Mandy has been cursed to grow whenever she's mean to someone. Needless to say, she's eventually several stories tall. Billy, however, rather approves of the situation.
"I like 'em large and in charge, mama!"
This little exchange from "The Loser from the Earth's Core":
Nergal: And so you see, Billy, I'm a sad, sad failure. I can't ever show my face in that household again.
Billy: Well, maybe you can show some other parts of your body.
In "Substitute Teacher", Nergal and Aunt Sis start nuzzling, before the camera rapidly cuts to show their son Nergal Jr. looking revolted as assorted... questionable sound effects occur from the off-camera antics:
Nergal Jr.: Ewww. Old people love.
in " Billy Gets an A" Irwin asks Mandy to be his study buddy, then continues to say "we can stay up all night together...studying".
In the go-cart race episode:
Billy and Irwin (singing): Well, we built our go-cart all by ourselves, and if you don't like it, you can go to...heck!
Dracula: Well, if you didn't make your babies so delicious, Dracula wouldn't have had to eat 'em!
In the same episode, Grim says "But you're a vampire, and vampires suck...blood!"
A rather interesting (and quite expected) one can be seen in the Halloween special "Underfist." When Hoss Delgado is freed from Mindy the Witch's binds, he readies his chainsaw/crossbow/fist thing and growls "Who wants the first spanking?" to an army of mutant brownies. If you look close, you can see one raise its hand...
Grim's rather macabre phrases can be considered the next best thing to mentioning death in the show.
Come on, Mandy. This should be fun... like watching a train wreck.
(laughs) This is more fun than the French Revolution!
One particular episode involves Mandy entering a portal the leads to... Irwin's bathtub, which Irwin is currently using. Instead of being horrified or embarrassed, Irwin is ecstatic that "dreams do come true".
In episode "The Good, The Bad and the Toothless" At the very end of the episode Billy finally gets his cash from the tooth fairy. It is a giant wad of dollar bills and Billy shouts "Im going to go show Mandy my wad". Immediately after that during the credits billy is running towards the tooth fairy and he keeps shouting "Coming" over and over again.
In the the episode "Five O'Clock Shadows", Billy meets a even stupider version of himself, who happens behaves like a stereotypical special needs child by making loud noises and wearing a football helmet.
Billy to Grim in 'The Show That Dare Not Speak Its Name': "Now bend over and let me RIDE YOUR HUMPS!" Granted, this was immediately following a flashback of him hallucinating that Grim was a strange camel creature, but it still fails to sound innocent in all regards.
"Mandy Bites Dog": Mindy calls her dog, Li'l Delicious, a tramp after seeing her getting married to Cerberus.
In "Here Thar Be Dwarves", Billy has an encounter with Yogi Bear and Boo Boo, who are depicted as junkies. Yogi Bear is seen with bloodshot eyes, a torn hat and tie, scratching his arm, and desperately trying to steal Billy's "pic-a-nic basket", even chasing after him. Boo Boo is seen with dark bags under his eyes and gives the impression of being high. Luckily for Billy, they stop when he enters a cave, since the bears fear caves.