Ye of little sex rejoice: for at least some of the ancient Greeks, there wasn't anything less virile than screwing around.
Michel Foucault's History of Sexuality spans a wide variety of topics, examining ancient to contemporary Western discourse on the sexual act. Specifically, it examines the origin of what we know today as "sexuality": a biological, psychological, and historical area of study that has been delineated as somehow above or apart from the rest of human activity. How and why did the canon of "proper behavior" in Western society place not only the sexual act, but constant discussion and definition of the sexual act, at the core of its being? Volume 2: The Use of Pleasure reviews ancient Greek texts on the erotic, dietetics, and other subjects to give perspective on the origins of "sexuality" by examining aphrodisia - the latter not particularly synonymous with the former, as difference in respective ideas of "virility" show.
Anyone with a passing knowledge of Aristotle's Nichomachean Ethics digs his focus on virtue through "moderation". (That's sōphrosynē to you classicists.) In between two given behavioral extremes, there's always a mean in between that the virtuous man follows (although it usually ain't the median between the two). So what quality did the virtuous man have that allowed him to more-or-less tread the moderate path?
"Mastery" (enkrateia), in short. In order for a man to be virtuous, his rational faculties had to hold sway over his sensual inclinations: he had to be a "ruler" (archontas) and not "ruled" (archomenous) in relation to himself, just like Plato's hierarchy. Now, the blatant sexism in that last sentence is intentional - in fact, it's key to the whole process here. When we're talking virtue in ancient Greece, we're talking about men. Whether that's being a good citizen of the polis, a kick-ass Athenian general, or even a wise slave of the Stoic sort, it means being manly. Enkrateia was (in addition to being the power of a king over a subject or a lord over a slave) the same sort of "mastery" that a man had over his wife and household, and that the "top" in a sexual encounter had over the "bottom".
This isn't to say that virtue wasn't expected of women or that they couldn't have enkrateia or sōphrosynē, but that "this virtue was always referred in some way to virility. . .there was also a structural reference, since in order for a woman to be moderate, she had to establish a relationship of superiority and domination over herself that was virile by definition." (Foucault, p. 83) A virtuous woman was a manly woman, in the womanly fashion of being manly. (That make sense? Good.) The way Greek morality seems to be ordered, no matter whether one was "ruler" or "ruled" in relation to Athens, one was obligated to set up the same hierarchy inside oneself with one's rationality at the top. You had to kick your own inner ass - and make all those worrisome inclinations towards the extreme (quite literally) your bitch.
Now, aphrodisia (remember Aphrodite?) was subject to one of these dichotomies and had a moderate mean to follow. (It must be stressed that this wasn't particularly parallel to sexual virtue as a later, Christian concept: the exercise of all virtue was dependent on individual situations, and whether it was virtuous to freak nasty or not could even depend on whether you planned on taking your supper late that evening.) The mean in question was between being completely desensitized to erotic and sensory pleasure (something that Aristotle admitted to be extremely rare) and its opposite: chasing every tail that wagged your way, and sometimes a few that didn't.
That means that if you were prone (like a great many of the contemporaries of Socrates, Plato, and Aristotle) to all sorts of wacky sexual adventures, even with women, you weren't particularly virile. In fact, you vere a vussy girly man, ja! Of course many folks would have the inclination to stick it in wherever they saw an opening; what made you a virile master of yourself, and thus a virtuous person, was to know when to go at it and when to let it be. What this meant for ancient Greek sexual ethics was manifest in its differences with modern ideas about being masculine or effeminate.
The dividing line between a virile man and an effeminate man did not coincide with our opposition between hetero- and homosexuality; nor was it confined to the opposition between active and passive homosexuality. It marked the difference in people's attitudes toward the pleasures, and the traditional signs of effeminacy. . .were not necessarily associated with the individual who in the nineteenth century would be called an "invert", but with the one who yielded to the pleasures that enticed him: he was under the power of his own appetites and those of others." (Foucault, p. 85)
If you were a pretty boy favoring ostentatious dress and perfumery, if you didn't like to participate in suitably manly sports, if you were prone to malakia ("softness" in the sense of being unmanly, but also associated with disease and sickness), then it was just as likely that you were hounding the ladies as it was that you were hyperactively homosexual. What you were doing was failing to be a man to yourself by not standing up to the ways your body was likely to lead you astray, and that tended, in the Greek mind, to manifest itself in the way you talked, how healthy you were, how successful you were at raising children, and so on. If your inner hierarchy was a shambles, it was likely to show in how well you acted out your role in the hierarchy of Athens and the rest of the external world.
These ideas led to a lot of conclusions that were seemingly alien, and yet very related, to later Christian ways of looking at sex and society. Medieval thinkers often looked to the pure and innocent virgin young woman as the epitome of sexual morality. Such a person without sin would have nothing to confess, and was thus free of taint in the Church's eyes. There's a reason why Sir Galahad was raised by women into a virginal lifestyle and thus was able to get his hands around the Holy Grail, while Dear Daddy, the ultra-masculine womanizer and beloved friend to the rough-and-tumble Knights of the Round Table, had to kneel at the entrance to that sacred Mass. Yet Christianity's association of constant sexual self-control with power above that of one's fellow man is at least akin to enkrateia, if far more demanding of restraint. Its means of dealing with sex as a discourse of guilt and confession to God through the Church is also heavily related to the medical and social dedication of Greek texts to aphrodisia as at least one physical aspect of his life where a man could display virtue.
And, of course, to the Greeks, practice made perfect (hence some Athenian philosophers' admiration of brutal Spartan child-rearing practices designed to make young men into young soldiers). Mastering the genitalia was a lot like mastering an instrument, or rhetoric, or a certain sport: that is, you pursued virtue in that field as a unique individual, making some mistakes and trying your best while (if you were wise) learning as you went. The right amount, method, and partner(s) in one's sexual life had to be gauged independently through "growing experiences", as we say nowadays. So while Aristotle might not think that all those letters to Penthouse about how you slept with four Roller Derby sex goddesses at once made you a big virile hunk o' man, he could at least be content that you'd gained some valuable insight into who'd be in your motel room the next time around.