the sickening inadvertent vulgarity of heterosexuals, even heterosexuals you like...

Understand please, I like Isaac Asimov.  I rarely have the slightest quarrel with him about taste or manners--but his painfully contrived limericks about what he'd like to do with clones of himself are not only not funny, they're icky.  As only an unreflecting heterosexual can be icky.  

Fact is, identical twins are essentially clones of one another--and what everyone wants to know is ¿do they fuck one another?  I think about half do; the other half walk around with strained little smiles, waiting for someone to ask the question.  I was pretty sure that the Patriota twins, Marcio and Marco, fuck one another--Well, why wouldn't they?

But in fact they don't.  

Because, if you follow their first or second two-minute "viral" videoclip to near its end, you see the angelically beautiful twain brethren Patriota responding to the word "beijo" ("kiss"), first questioning, then as they look into one another's eyes hardening with absolute brotherly amused disgust into "no way ever in Hell, kissing or fucking."

You see, my dear Isaac, he who proposes fucking a clone, is proposing to fuck an identical twin, and, in effect, is proposing to fuck himself--which is too close to violation of the Incest Taboo to be borne (by the dominant half of us who would no way, ever, if he had one, fuck a brother).