In this scene from the movie Decoys 2, an evil alien transforms into a sassy dominatrix so she can mate with a young guy. It's just one of the most embarrassing alien mating scenes ever.
I thought Evil Aliens had the most heinous alien impregnation scene... until I saw 1981's Inseminoid, a low-rent Alien clone. And yes, this alien has a bong for a penis. Clip is NSFW.
Why does science fiction love extra breasts so much? Blame Douglas Adams, who threw in a reference to the triple-breasted whore Eccentrica Gallumbits in Hitchhiker's Guide to the Galaxy. It sounded all sophisticated and sly coming from a Brit. But then William Shatner and Paul Verhoeven got their hands on the concept.