An episode where Londo Mollari was shown cheating at cards by using a tentacle to surreptitiously grab extra cards from the deck. Turns out that the Centauri tentacles are not just tentacles: Centauri males have six prehensile penises. That are each 2-4. Feet. Long.
More amusing was Vir's bumbling attempt to describe to Ivanova (while asking her relationship advice about Lyndisty) the varying... levels of intimacy a Centauri couple could encounter while necking (a misleading word in this context if ever there was one), complete with sound effects and gestures indicating the difference between "one" and "six":
Vir: There were other women, but I never got past one. Ivanova: You mean first base. Vir: No, no, I mean one. You see, we have six, ah... we have six, you see, and each one is a different level of intimacy and pleasure. So, you know, first you have one, and that's... nnyeahh. Then there's two, and by the time you get to five it's like (starts panting loudly)...
Also, Word of God has stated that Centauri females also have six, er, receptacles — three on each side of their spine.
The original script for "Born to the Purple" called for a close-up of Adira's back, complete with "holes." Unfortunately, the show's very low budget nixed it.
Londo was furious that the action figure version of himself sold in the station gift shop lacked the relevant characteristics. Ivanova, who has an unfortunate knack for finding herself involved in discussions of Centauri anatomy, says "So you feel you're being symbolically cast... in a bad light?"
In the pilot episode, G'kar tries to hire the human telepath Lyta Alexander to bear his child, because the Narn have no telepaths. "Now, would you prefer to be conscious or unconscious during the mating? I would prefer conscious but [grins] I don't know what your pleasure threshold is." Indicating that the two species' reproductive organs are similar enough for copulation. Which makes rather perplexing a later episode where G'kar is shown having an affair with one of Londo's wives. I mean, given what we know of Centauri "attributes", that's not like a human having sex with a sheep, it's like a human having sex with a spider.
Several years later (and after the full awakening of her Touched by Vorlons powers) Lyta agrees to provide G'kar with her genetic material, commenting in passing "Oh, and you once mentioned wondering what my pleasure threshold is. I just recently found out... I don't have one. Have a very, very nice day."
G'Kar is also described as having a fetish for human women, and his promiscuity is referred to in several places prior to his first imprisonment. For example, in Na'Toth's first episode, when G'Kar asks her to investigate how a black tulip turned up in his bed, she comments "It is not my place to speculate on how anything finds its way into your bed," within only a few days of her arrival on the station, suggesting his reputation is well known on Narn as well.
Another incident involved a visiting Narn official finding a pair of panties on the floor of G'Kar's bedroom. G'Kar's response suggests that he's mostly irritated that he didn't have time to police the room for such items before the visit.
Given that human beings have figured out many fun things beyond standard Tab A into standard Slot B, G'Kar doesn't necessarily need physical compatibility for any of his extra-species dalliances, just creativity and dexterity.
It's heavily implied that most species have been directly genetically manipulated by The Shadows and/or the Vorlons. Given the lack of telepaths is ultimately revealed as being a far more crippling disadvantage than implied by not having your own mindreaders for intergalactic politics, it's a safe bet that the Narn are just one more species only a step or two away from LEGO Genetics.
Londo in particular, but also G'Kar and others, make insulting comments about other male characters' lack of sexual prowess.
Indeed, Londo and G'Kar get into an argument about G'Kar's late arrival that quickly diverges into a conversation about premature ejaculation. Much to G'Kar's increasing horror.
They also managed to sneak in an implied and later explicitly confirmed relationship between Ivanova and Talia, and a (pretended) marriage between two men was seen as completely normal by every character in the show.
Let's not forget Londo talking over a comm-link to someone severely annoying him, who then ended transmission with "I'll be in touch." Londo's response? A self-grope with both hands, meaning he grabbed his own abdomen, as he said, "touch this!" Viewers who missed the previous...explanations for Centauri genitalia were probably confused, and any of those viewers who might've added it up were probably quite horrified without the benefit of the previous explanation to ease them into the information.
Actually, that was at the beginning of the episode ("The Quality of Mercy") where we first learn about Centauri male "attributes" — only in retrospect or on subsequent viewings does it become evident that Londo just made a presumably obscene gesture.
It's a bit hard to tell with Londo's accent, but it's more likely he said "Touch these." Considering the Centauri don't seem to be as modest about their sexual characteristics as humans tend to be (Londo openly displays a statue of a naked hermaphroditic woman, who's a goddess no less), it's possible that what he said is no more offensive than "kiss my ass" would be to humans.
Then again, it may be why Centauri men favor vests and long coats (at least around aliens). There are examples within canon of Centauri passing as humans for espionage purposesnote (in fact, they tried to claim Earth as a lost colony when they made first contact) so keeping their genitalia under wraps may be important for strategy as well as modesty.
We do have nude statues of various deities in our human cultures, you know?
That was just one example. Another comment made by Londo seems to indicate that Centauri expect their dolls to be anatomically correct.
In the episode "The Illusion Of Truth", Londo and Sheridan are arguing about the climate control in the former's quarters:
Londo: I do not mean, "oh, I think I will put another blanket on my bed tonight", I mean "look, my left arm has snapped off, like an icicle, and shattered on the floor!"! This is highly inappropriate, Captain!
Sheridan: I agree. There's several other parts of you I'd much rather have snapped off.
In "Convictions", Garibaldi tells Zach to explain the "missionary... position" to some Drazi clerics.
In the spin off Crusade one episode involves a human/pak'ma'ra porno that is apparently VERY attention getting.
The characters further imply when two different species hook up some um...gadgets might be involved.
One of the characters viewing the video mentions that humans and pak'ma'ra can't POSSIBLY do what it is being indicated they are about to do (becuase of, shall we say, plumbing problems)...then, apparently, they do anyway. (The file was one of several on the crystal. The most apparently straight-laced of the characters turned out to have a collection of such stuff, and mixed up his crystals when turning in a written report.)
Rather, the report was on the crystal, but he forgot to erase the previous data, so that the porno started as soon as the report ended. It makes one wonder if Max either a) had a shortage of empty crystals at the moment, or b) he's got so much porn he can't keep track of it all.
During Marcus' and Franklin's trip to Mars, in a very shoddy cargo hold, Franklin says that it "smells like the inside of a Martian pleasure dome on Sunday morning".
Of course in this case, Mars is populated by humans instead of Green Skinned Space Babes, and "pleasure" could mean anything from drugs to sex to all-night raves... Or something that doesn't involve drugs and sex. But then, there's nothing to say that it doesn't mean that.
The "Sunday morning" part would seem to indicate that something illicit and/or immoral is going on. It was established in Season 1 that Catholicism has some sort of presence on Mars: Sinclair is from Mars and makes more than one reference to having lived among Jesuits at one point.
What really sells the "sex" aspect is Marcus's response, "I wouldn't know about that..."; he had been earlier mentioned to be waiting for the right lady.
Followed soon after by Ivanova disappearing, the Political Officer walking into the room still nude, and Sheridan glancing down before declaring that it must be colder in here than he thought...
The Starfury pilots, like Real Life fighter pilots, have various patches on their uniforms. And, just like Real Life fighter pilots, many of those patches are full of Double Entendres. Of note is the patch worn by all of B5's pilots, showing a Starfury being launched (via being dropped through a hatch in the "floor" of the station), with the words "Ugly, But Well Hung." It's plainly visible through much of the series, because none of the censors ever looked closely enough to notice.
JMS posted to Usenet as season 4 was getting under way that he only just realized there simply weren't any censors.
In a second-season episode, one of Londo's wives calls another one a "bitch". Fans asked Peter David (who wrote that episode) how he managed to get that word on the air. He responded "I didn't. I just put it in the script."
In the first season episode "Infection" Garibaldi is trying to decide if he should buy some item from a shop.
"According to the translator, it's either an aphrodisiac or a floor wax. I can't decide if it's worth the risk or not." And upon deciding to buy it, "If this thing leaves a waxy yellow buildup—on anything—I'm coming back here."
There's also Ivanova's "human style" sex ritual to seal an alliance with the Lumati.
"Anatomically impossible, Mr. Garibaldi, but you're welcome to try."