Tahno: (in an extremely suggestive voice) Y'know, if you'd like to learn how a real pro bends... I could give you some private lessons.
Korra isn't too heavy on the subtlety herself:
Korra: Yeah, but when you're with her you're thinking about me, aren't you?
After Bolin catches Mako and Korra kissing, Mako finds him drunk at a bar. On noodles, not actual liquor, but the viewer can put two and two together here.
The next day he acts hung over, and "loses his noodles."
It's also worth noting that sake (Japanese rice wine) is sometimes served in a bowl.
"And the Winner is..."
Tenzin: Lin, with so much on the line, it would be nice if we could help each other out, at least for one night. (emphasis added) Lin: Like old times? (Now she's behaving all Tsundere) Tenzin: Like old times. (Look at his face) Lin: Ok, I'll try to be less abrasive than usual. (Emphasis is in the dialogue)
Oh, and speaking of Amon's Memetic Molester behavior...If that scene where Amon removes Tahno's bending doesn't count as that, then I don't know what does.]]
In general, all of Amon's scenes where he removes someone's bending either contribute to his Memetic Molester status or look like some kind of public execution.
"Skeletons in the Closet"
Tarrlok's and Noatak's backstory plays up much like a tale of child sexual abuse, with their abusive father bringing them along with him on "hunting trips" away from their mother and making them perform acts that Tarrlok sees as degrading and viscerally wrong. Noatak ends up chillingly stoic and seemingly depressed, being the father's favoured plaything, and ends up committing said acts with less resistance... until he violently retaliates against the father and tries to run away.
Book 2: Spirits
Ginger's demonstration of what the new invention of movies (or movers, as Varrick calls them) can do. We get the distinct impression that Varrick is looking to go into stag films.
In real life, when "moving pictures" were first getting popular, they were often used as ways for people to view "mature" material. The Rule of First Adopters, and all that.
Also a Shout Out to Aang's use of it when they first visit the Fire Nation in season three.
Bolin shouting "My instrument!" after Mako heats up the hot tub water to the max.
Doubles as a Shout out to Toph's "delicate instrument" line in the original series.
Ping questioning Mako on dating Korra. His tone of voice and Mako's reluctance to speak on the matter make it sound a lot like he's asking him how the sex is.
Ping: Come on, if I was dating the Avatar, I'd be telling everyone about it!
"A New Spiritual Age"
As one can see from the page picture, it's shocking on how they got away with showing a genuine human corpse in a more realistic stage of decay (likely naturally mummified by the dry desert air) instead of using the typical bare-boned skeleton. Good thing the shot itself was quick...
"Night of a Thousand Stars"
In the "Nuktuk" movers, Naga's character Roh-Tan had a dubbed voice with the Verbal Tic of adding "Nuk" to the beginning of or in front of some words, such as "Nuktastrope" instead of "catastrophe". A sneaky Unusual Euphamism version of this trope is arguably used during Pabu's character Juji's death scene in the final mover: Roh-Tan's reaction is "Nuk No!"
Watch carefully when Korra and Asami's car stops in the middle of the road during Korra's driving lesson. The frustrated driver behind them passes them, and very subtly moves as if to flip them off right before he moves out of the shot.
Korra's talk to the new airbender in the bridge sounds suspiciously like she's talking him out of committing suicide.
Ming-Hua and Ghazan are rather liberal with their mutual battle tactic of throwing their opponents into molten lava.
"The Earth Queen"
P'Li is said to have been in a relationship with Zaheer. When Zuko shows up to check on her, she figures Zaheer must have escaped and, in the most treacly voice she can muster, quips "I'm feeling warmer already."
When Korra asks Tenzin about how the Earth Queen's like, his answer seems like a Last-Second Word Swap from the "b" word:
Tenzin: I hear that she can be quite [beat, with a suspicious "a" sound] demanding.
"The Metal Clan"
Lin and Suyin are half-sisters, which is unusual for a cartoon but not unheard of. Less common is the fact that neither met their fathers, which raises some interesting implications about Toph's love life.
After seeing Zuko's dragon, the airship captain heads off to get a drink.
P'li is shown lounging around with what looks like a martini.
"Enter The Void/Venom of the Red Lotus"
The number of deaths and near deaths in these two episodes was quite a lot for a Y7-FV show. Doesn't help that two actual deaths are on screen. Though apparently head exploding is still off limits for Avatar.
It's also notable for the heroes intentionally killing their foes. For once in the Avatar series, Bad Guys Do the Dirty Work has been averted.
Word of God has confirmed that Ming-Hua is dead. What hasn't been confirmed is whether she died in the cave-in or when Mako electrocuted her. If the normal rules of electricity apply here (Harmless Electrocution has happened before in the Avatarverse, but it's been averted more often than not), it's almost certainly the latter.
The "metallic poison" the Red Lotus used on Korra is mercury, and mercury poisoning is, suffice to say, a very nasty way to go.
Eska states that ordering a suite with only one bed for her and her brother was not a mistake. Apparently the show no longer shies away even from blatant Incest Subtext. Then they pull a bait-and-switch by revealing "Desna sleeps in the tub."