Accidental Innuendo / My Little Pony: Friendship Is Magic
The show in general is a goldmine of accidental innuendo, and it is hard to tell what is completely by accident and what might not be. YouTube users like kyrospawn and EpicGteGuy are known to take MLP:FIM clips out of context for a variety of purposes, but one of them is to highlight how sexual they seem out of context.
Same deal for screencaps; after any given episode airs, it's common to see tons of freeze frames that look really dirty out of context. Such as this or this. It really doesn't help that the blinking animation (which is used a lot), almost always looks like "bedroom eyes" when paused halfway through.
Rarity's shop includes bridles (one is even shown on Carousel Boutique's sign), as seen in various episodes (such as "Swarm of the Century", in which Twilight calls outfits incorporating them "gorgeous") and other official materials (such as Adventures in Ponyville, in which Rarity and Applejack wear them). Given that ponies don't even wear them while pulling carriages ("Over a Barrel", "The Best Night Ever", etc.), it makes you wonder just what they are supposed to be used for...
Rarity is lounging in a hot tub, with a look of sheer bliss on her face. Cue Pinkie rising out of the water in, um, questionable proximity to Rarity....
Alternatively: "I have located the water jet."
In the same episode, Twilight Sparkle's horn becomes floppy with blue dots on it. The way it flops around is reminiscent of, well... you get the picture. The way Spike stares at it on the verge of cracking up almost implies he's in on the joke.
In "Winter Wrap Up", due to where Spike is sitting during Twilight's first verse in the "Winter Wrap Up" song, it's easy to see how he might be doing something else entirely. The way he bounces while Twilight is walking along does not help.
A squicky example occurs in "Feeling Pinkie Keen" when ponies are running away from hydra, and Spike is seen sitting on Twilight's head right in the place where her horn should be, which is nowhere to be seen, and there's an expression of pain on his face. (Not to mention he's positioned there suspiciously firmly considering they were running uphill at high-speed.)
The end, in which Rainbow Dash flies off with two (male) members of the Wonderbolts and declares "... I've got plans!", could be taken as this.
That same episode also opens with Fluttershy recapping "the elements of a good cheer": "loss of control", "screaming and hollering", and "passion". Taken out of context, it kinda sounds like she and Rainbow Dash are talking about... something else. Not to mention that it's given out of context, with no explanation until afterwards.
A visual version happens in the "Over a Barrel" episode. In one scene Rainbow Dash's wings are folded but after Pinkie Pie comes out dressed as a showgirl, they are wide spread. Previous episodes showed that this sort of reaction from her (one moment they're folded and then next they're spread) is a sign of excitement. Considering Rainbow Dash has considerable amounts of Les Yay and is often thought of as be fans to be a Lesbian Jock, it's been thought she was... excited when Pinkie came out.
Spike remarking, "I gotta show Rarity the crown jewels."
To get the Wonderbolts' attention Rainbow Dash catapults a male pony into the air and "saves" him from the fall by catching him on her back... and if you cut the last scene out of context, it suddenly starts looking completely different. It doesn't help that Rainbow's expression looks really dirty.
In "Lesson Zero", Twilight tries some armchair psychology on Rainbow Dash when she thinks Rainbow is angry at Applejack, and tells her "Oh, Rainbow Dash, you don't have to hide your feelings from me." TwiDash shippers took notice. It doesn't help that she delivered that particular line in this◊ pose. Some AppleDash fans also interpreted the scene as Twilight being a Shipper on Deck.
Rainbow Dash tells Twilight that her inability to understand the difference between "coolness", "awesomeness", and "radicalness" is why she would never qualify to be her pet. Errmmm...
Also, Rainbow Dash suggests that she wants a pet; Fluttershy acts a little...too excited to this response, to the point that her exhales of joy sound like orgasms. Not to mention that she tells Rainbow Dash that the animals will love her, and that they (Rainbow Dash and Fluttershy) will "be best friends forever and ever." See it in all it's creepy glory here!
The sounds of Amethyst Star opening a jar of peanut butter off-screen, can sound... different. Let's leave it there.
When Rainbow Dash pulls in Applejack for a photo opportunity, the positioning of the mouths and Applejack's reaction afterwards suggests something a bit more than being pulled into shot, which the fandom has noticed.
In "Family Appreciation Day", Filthy Rich is embarrassed by his first name simply because... well... it means "mucky" or "messy" after all but it isn't hard to think it also makes him sound like a porn star... especially when he just gets "Filthy".
Cherry Jubilee is styled like a "madam" of the Old West, and being "boss of Cherryhill Ranch" may give a few different visions of what actually goes down there. Not to mention she can always use "a pony with quick hooves and a strong back".
A Singin' in the Rain tribute in "Hearts and Hooves Day" wound up being mistaken by some for a pole-dancing joke. What made this particularly foul was that the tribute was done by Sweetie Belle, of all characters.
"A Friend in Deed": A cow that drinks milk would be like a grown woman that drinks breast milk.
"Magical Mystery Cure" has Spike's "Gangnam Style" hopping, which Psy explained as a "horse-riding dance", seems to suggest that Spike likes "riding" ponies...and the mares in Sugar Cube Corner thought it was cute.
Rainbow Dash: "I did tricks with that flag the likes of which no pony saw before."
The last time Miss Harshwhinny gives Rainbow Dash a dressing-down for her "over-enthusiastic outbursts", she literally gets up in Dash's face, appearing to kiss her on the muzzle. Slashfics in three...two...
Diamond Tiara referring to the CMC as going to be in "a hot mess".
While on the train, before going to comfort Scootaloo, Rainbow Dash says "I can't hold it in. I want you to win so bad!" with an extremely dirty expression on her face. This line and expression, when taken out of context, can make it seem like Rainbow wants to do something else with the Crusaders. Even in context it sounds rather perverted. It has gotten much lampshading on the popular imageboard Derpibooru.
In "Power Ponies", Applejack's alternate persona of Mistress Marevelous combined with her mastery of a psychically-controlled lasso can easily be seen as Fetish Fuel.
It only lasts for a few frames, but during the performance at the school Big Mac can be seen staring and sweatingnote More likely due to the fact he's having trouble keeping up with Fluttershy's ad libbing at Fluttershy while she's shaking her butt.
While this isn't the first time a mare has been pinned on her back in the show under another pony, the shot of Pinkie Pie over a sobbing Fluttershy could easily be interpreted very badly if viewed out of context.
At one point, Fluttershy dresses up like a bee and asks a swarm of them if it "brings to mind any images" for them while wiggling her butt at them suggestively.
"I LOVE new ideas that make me feel funny at first!" Oh, Pinkie...
While the town is gathering to watch the Breezies, Spike can't see them due to many ponies in front of him blocking his way. We're treated to some gratuitous views of the ponies' rear ends and Spike's excited expressions surely don't help.
When Party Favor makes his balloon binoculars and the balloon bridge, the shot shows him sitting down on his haunches, working his hooves feverishly in front of him to produce the final work. However, the shot cuts off just below his torso and the action in his hoofs just out of shot and blurred enough to make it look like he's working something else...
When Applejack gets her cutie mark back, the first thing she says is "Finally I can buck like a five-bit snake herder at an Appleloosa ranch house again!" It isn't immediately obvious to most viewers what bucking has to do with snake herding, or why a snake herder's services might be needed at a ranch house...
In "Castle Sweet Castle", as Twilight wakes up, she pierces a pancake with her horn and it dangles there covered in whipped cream.
In "Slice of Life", Octavia and Vinyl make "beautiful music" together. This involves a lot of longing looks, Octavia undressing, and suggestive smiling between them. It's almost borderline G-Rated Sex.