Yes, the evil aliens in Decoys (and Decoys 2) mate by sticking their tentacles down a human male's throat and then impregnating him with their eggs. And for some reason they have to use their shapeshifting and telepathy to turn themselves into the guy's ultimate fantasy first - so he'll be really, really excited. And the mating must take place at sub-zero temperatures. Got it? Good.

The most awkward scenes of alien mating run the gamut from cheesy space-opera mating to full-on I-can't-believe-they-went-there porn. And yes, some of the clips below are not work-safe, so exercise discretion.

Star Trek: The Next Generation:

Trek, in all its various incarnations, has always been full of unfortunate alien mating moments. But for my money, this is the worst - it's actually the scene that inspired me to track down all the rest of these clips. Riker, blessed with the power of Q, decides to give Worf a Klingon girlfriend... who crawls around the Enterprise bridge in a Klingon aerobics instructor outfit. "Is this your idea of sex?" Geordi asks, awestruck. "This... is... sex!" Worf howls. Ummm. yeah.

Breeders:

Oh dear. An alien has been capturing women and attemting to mate with them. Here they are, in the alien's mental thrall, coating their naked bodies with its extraterrestrial sperm. And yes, it's NSFW:

Futurama:

Poor Dr. Zoidberg. His "erotic display" just doesn't turn out that well.

Weird Science:

In one episode of the short-lived TV series, their friend Chet starts dating an alien woman. Unfortunately, she wants to devour him after sex. Luckily, his ex-girlfriend intervenes just in time.

Babylon 5:

A similar mating practice crops up in this scene from B5's pilot. Commander Sinclair, he's a life-saver.

Space Thing:

An alien in human form, Col. Granilla, comes aboard a human spaceship commanded by women. It's up to this nice Kansas girl to teach him the ways of human mating. Clip is NSFW:

Something Is Out There:

Hand sex! Maryam D'Abo comes from an alien race who keep their erogenous zones in their hands. Here she is, getting it on with her boyfriend before their ship suffers a prison break. Clip is very work-safe, unless hand-sex offends you.

Quark:

This Star Trek spoof featured an episode where Ficus, the unemotional plant man (who's the counterpart of Mr. Spock) has to seduce Princess Libido, who's fallen in love with him. His objective is to use his sexual wiles to convince Libido to help him and his crewmates escape from her evil father. There's just one problem: Ficus doesn't have sex like normal people. He reproduces by pollinating. He's only too happy to show Libido how.

Species 2:

Eve, a clone of Sil, gets so excited she squishes a baseball. It's all because an astronaut, Patrick, has brought something alien back to Earth with him, and it manifests itself while he has sex with a debutante, and then her sister. The debutante suddenly gets very, very pregnant, while the sister notices that Patrick is growing rather a lot of tentacles during sex. Later, Patrick and Eve get together, and Eve's nipples grow tentacles, which I've never seen before. Clips are very, very NSFW:

Society:

Walking in on your parents having sex is bad enough — but what if you've learned your parents are aliens, who have sex by melting their flesh and blending together into weird and monstrous forms? And your sister is also an alien, and her head comes out of your mother's crotch? And asks you if you have any Oedipal fantasies? You might be put off sex for quite some time. This clip may actually be work safe, hard to say.

Inseminoid:

A human gets tied up and subjected to mating with an alien whose penis is a giant bong. This NSFW clip already featured as a "found footage," but I had to include it for completeness. Warning: very NSFW!

The Outer Limits:

Commenter Roklimber suggested this bizarre NSFW scene from a 1995 episode. Alyssa Milano is a nice college girl, until she gets hit with a spore from outer space. And then she suddenly wants to have sex with lots of guys... by absorbing them into herself.

Evil Aliens:

Nerdy Gavin finally gets to have sex with an alien woman, but finds out it's not all it's cracked up to be. And meanwhile, a woman named Foxy gets implanted with an alien fetus. And yes, it's NSFW.

Additional reporting by Alasdair Wilkins.

In Inseminoid, a team of archeologists land on an alien planet, and discover some weird crystals. Which make them go nuts, or something. They all start dying, in totally ludicrous ways. Then the ship's doctor, for some reason, injects Sandy with something and gets the bug-eyed alien to inseminate her. Afterwards, the now-pregnant Sandy goes around killing the rest of her shipmates, before giving birth to aliens. (Weirdly, the ship's doctor, and the alien that knocks Sandy up, both disappear from the film after the half-hour mark. You really only glimpse the daddy alien for about 20 seconds of the film, total.)

Inseminoid may actually be the worst] science fiction film ever made. Well, maybe not. But it's up there. Interestingly, it came out in the same year as Galaxy Of Terror, another entry in the disgusting pervy alien genre. [IMDB]