The phrase is Anne McClintock's, from her book Imperial Leather: Race, Gender and Sexuality in the Colonial Context. She is referring to the European tendency to sexualize the orient and make it into "a fantastic magic lantern of the mind onto which Europe projected its forbidden sexual desires and fears". McClintock has much of great interest to say, but I'm going to diverge from her book and discuss early writings which turned Siam into a porno-tropics, a process which of course continues to this day in Thailand.
One of the earliest porno-tropic texts about Siam I've seen was written by Thomas Herbert, who accompanied the English ambassador to Persia in 1627-9. On his return he wrote Some Yeares Travels into Divers Parts of Asia and Afrique... (the actual title is much longer, but this will do if you're looking to find it; I read a microfiche of one of the original copies at the University of Toronto library). This book had great vogue in its time, and was expanded and reprinted eight times in several European languages in the 150 years following its initial publication in 1634. His tome is an exemplary 17th century orientalist portrayal, managing to sound both salacious and pious in its description of the scandalously intriguing habits of the inhabitants of the non-European world.
Herbert's description of Patania, then a tributary kingdom of Siam, today a southern Thai province, brought together in one masterful paragraph all the characteristics of the oriental other: sensual, promiscuous, and effeminate, peopled by natives enslaved to the pleasures offered by climate and diet.
The men of note transcend in Curtesie; for at any mans arrivall, they blush not to proffer their Daughters or Neeces to be their bed-fellowes; yea to concomitate them at bed and board during his stay; the price for such a favour not equalling so high a complement: but that, were it lesse, too much in my opinion for such Pandars and base prostitutes. At the end of the prefixed time the woman returns home well pleas'd; so far from shame or losse, that they rather accompt her honored; and fit for preferment: But tis dangerous to be wanton elsewhere; jealousie on either side inflaming into rage, which seldom dyes without one or anothers destruction...Adultery they punish rigidly; Fornication is more tollerable. The young women are carelesly frolick and fearelesly merry; the married, melancholy and strictly observed: idlenesse and heat provokes them to inchastity. The men are also effeminate; yea wallow in all kinds of turpitude and sensuality: their females are often in their fight; the grape commoves them to wickednesse; they delight in their gust and pallat with choysest wines, waters, Rack, Ryce, and fruits, both succulent and restorative; and which make Venus predominate: but by this their intemperance they abreviate their dayes; few exceeding sixty yeeres; an old age, if you contemplate their lust (Deaths best harbinger) and the Zone they sweat in: bad, both; both, intemperate.
Herbert, who I can only think never visited Siam himself, reported that it is "famous for power, wealth, and many forts...The Zone is hot, the men black...and transcendent Idolaters". However, the bulk of his description was given over to fantastically lascivious details. He read moral proclivities from outward appearance in a particular way, equating scanty clothing with promiscuity. According to him, both sexes adorned themselves for sexual display in Siam: "Boyes paint themselves with a celestiall colour from top to toe and as an augmentation of beauty, cut, gash, and pinck their naked skins...the men affect perfumes." As for women, his "dull memory compels" him to write that they, "the better to allure men to sodomitry", were naked but for a "fine trasparent (sic) cobweb-lawn" about their loins which "by a base device is made to open as they go; so that any impure ayre gives all to mens immodest viewes". The allure was successful in Herbert's telling, for "to see a virgin here, at virgins yeeres, is as a black swan".
Herbert wrote that men had a gold bell, "in it an Adders tongue dried", placed under their foreskins to (somehow!) discourage sodomy, a practice "in foregoing times" popular. When intercourse was desired, he wrote, a midwife gave the man a "sleepid opiated potion" and "the Bell is loosed from the flesh, and fastened to the foreskin, which hinders not but titulates". This detail might have been supplied by Samuel Purchas, whose Purchas his Pilgrimage, or Relations of the World... (1617) was compiled, without leaving England, from travel accounts. According to Purchas, "The Siamites...weare two or three balls of Gold or Silver, as bigge as a Tennis-ball, in their yards".
Herbert's and Purchas' accounts cover much of the same lewd ground, but betray an intriguing discrepancy. In Herbert's portrayal, women are proffered to travelers by male relatives, while in Purchas' women offer themselves. This small difference may reveal the authors' unease with female sexuality and provide some clues to European men's ambivalent relation to the oriental - and the western - women of their imaginations. The scandalized tone they adopted may reflect more than prevailing European sexual mores which prescribed chastity - for white upper class women, at least. It could also point to the unmentionable scandal of European male desire for the native women they were supposed to disdain. Behind the conventional image of such women as unchaste and unclean lay a forbidden spectre of allure which seems to have haunted the imaginations of Europeans at home.
How could Europeans comprehend these women's purported sexual licentiousness? To construe the women as initiating sexual contact was both threatening and reassuring: on the one hand it deconstructed European gender norms, dismantling "natural" masculine and feminine gender hierarchy and thus symbolically emasculating European men; on the other it placed the onus for sexual indiscretions on the "base prostitutes" themselves, absolving men of responsibility and of guilt. Equally paradoxical was the construal of these women as under local men's control, for while "natural" gender norms were thus reconstructed on alien soil, the careful, and quintessentially orientalist, feminization of Siamese men was threatened.
And this determined feminization may have been vital to the masking of an even more unspeakable desire, one perhaps coyly revealed by Herbert's claim that the Siamese "have beene (in foregoing times) wicked Sodomites". | 
