Indeed, the definition of OTK is interesting. As Freddie points out, the term 'thigh boot' has definite sexual connotations, to say nothing of the boots themselves and so OTK has been embraced by high street retailers. And why not? They want to shift stock, move boots and over-the-knee is a far more agreeable term in a suburban, high street, non-fetish environment.
The movie Pretty Woman is more than 30 years old now yet it still casts a long, long shadow over the sales of over-the-knee and thigh boots. Over-the-knee boots (at whatever height up the thigh) are much in vogue this year, as they were last year as well, and if you read any fashion column or blog about this enduring fashion trend that movie is almost certain to be referenced somewhere in the piece - typically high up and generally in the paragraph where the author reassures her readers that they needn't fear looking like Julia Roberts ("Vivian") in Pretty Woman if they give in and buy themselves a pair of these trendy boots and then giving them advice on how to tone down the sexiness, and what works and doesn't work. Apparently Brokeback Mountain exerted a similar negative impact - for a while anyway - over the sales of cowboy boots. But nothing like the enduring power of Pretty Woman!
My own boots come an inch or two over the knee - the classic OTK boot. But being pull-ons they slouch slightly and so they really come to just barely above the top my knee cap. Both pairs are suede - one dark brown, one grey. I was reluctant to get smooth black leather - at first - because I really wanted to steer clear of any suggestion of fetish (I guess I was leery of the Vivian effect too) I am more comfortable with wearing OTK boots now - totally at ease in fact - and so have plans to pick up a pair in black calf. These will be slightly lower still - 52 cm shafts instead of 58 or 60 as my other two are. With ankle zips they shouldn't slouch though.
When I wear them I make a point of dressing casually but neatly - jeans and jumper, nice shirt, generally sober colours, nothing flamboyant. A simple masculine look that avoids dandiness as well as androgyny.
Thigh boots never really appealed to me, let alone crotch boots. They are far too fetishy for my tastes.