Note: This section is only for the 60s and 70s, when the Avengers were under the rules of The Comics Code. The modern Avengers have no "Radar".
After his return, Captain America was obsessed with killing Baron Zemo, to avenge Bucky. And he meant it, each time he got near him, he goes for blood. He was very close once, but the Executioner attacked him from the back. And then, he headed to a final battle, to settle things, to kill him once and for all; even the main page promised "Now, by my hand, shall perish a villain"... but there's a problem. Captain America shall not kill. So, in the final scene, he used his shield to reflect the sun and blind Zemo, who began to shoot blindly, caused a landslide, and died. Captain America could then gloat that Bucky has been avenged, and still stay capable to say that Zemo's death was his own fault.
The Wasp, always flirting with Hank, was certainly borderline. But it was carefully played: she managed to seem a Lovable Sex Maniac without actually making references to sex.
The Scarlet Witch, a girl whose costume is basically a swimsuit, was a bit too sexy for the time, but it helped that only her face was visible, and the convenient cape prevented having to draw that part.
Not to mention the pink bodysuit she wears underneath.
The time when Korvac and Carina fused their bodies and souls during the "Korvac saga". It was basically about Energy Beings "having sex" than about an actual physical action, but the face of Carina was so... you know...
The first appearence of Wonder Man, who died at the end of the issue. It was arranged so that he died because Zemo did not gave him a medicine in time, wich is a bit of a technicism, but less evident than if Zemo actually shot him with a special weapon or something like that.
The Sons of the Serpent, who were basically a Captain Ersatz of the infamous Ku Klux Klan. As Stan Lee could not make a direct mention of racism, the Serpents spoke in vague terms; but in terms that were both vague and highly explicit. Consider this quotation: "Say it with me, America! Let all repeat the sacred Serpent oath! "As the first serpent drove Adam and Eve from Eden, so shall we drive from this land the unfit, the foreign-born, the inferior! We are the sons of the serpent!"". As you see, there is no mention to black people or white supremacy, but you would have to live inside a bubble for not reading between the lines... specially if you were in 1966, with the racial conflicts as a very real and tangible real-life topic, and with Malcolm X and Martin Luther King still in the newspapers instead of in the history books.
In Avengers #51, the Wasp is having fun in her pool, wearing a bikini... and the Avengers were kidnapped right there, without her having time to put some clothes. And so, she stayed the whole issue fighting in a bikini. Sounds as very little now, but that was in 1968.
Mantis was wounded during a fight with the Zodiac, but her great self-control works as a sort of Healing Factor. She's taken to her bed, and her boyfriend, the Swordsman, stays with her.
Vision:She's a great woman, Swordsman. Even hurt, her control of her body and mind nears perfection.
Swordsman: Yes, Vision, I know.
Vision: I'm sure you do. Good night.
Avengers 200 introduces Marcus Immortus, the son of Immortus, trapped alone in Limbo since his father's death. To escape to Earth, he needed to be born in Earth, teleporting was not an option. Selecting Ms. Marvel to be his "mother", for her unique strength, he teleported her from Earth to Limbo, seduced her, and "with a subtle boost from Immortus' machines", she accepted being impregnated by him. Or, in layman's terms: he kidnapped her, drugged her and raped her. In Avengers Annual 10, free from Marcus' mind control, she gave a monumental What the Hell, Hero? lecture to her former teammates.