In Japan and many other nations in East Asia, regular bathing was normative for much of history. Musashi Miyamoto was famously attacked while he bathed, back in the 1500's. Similarly in Rome, at least among the upper classes, frequent bathing was normative.

Moreover, while "bathing" in the sense of fully immersing oneself in water, or pouring water over oneself, was often difficult to accomplish due to fuel expenses if nothing else, washing with a wet cloth was doable. There's some reason to suspect that in Japan even among the nobility bathing wasn't common until after the Heian Period (the Tale of Genji never mentions bathing, but then it never mentions food either, so we can't take its omission to mean that people didn't bathe) EDIT: I am wrong and badly so, Genji does mention bathing.

But by the Kamakura Period (~1185CE) there's records indicating that bathing was commonish. One hot spring claims to have been used for over 3,000 years, though that's not really verifiable. But there are records indicating that at least the upper classes had baths in their homes by the Kamakura period.

The image of people in prior eras as filthy and never washing is largely a myth. As for oral sex, even without bathing, wiping your junk off with a wet cloth would reduce the disgust factor significantly.

hi! not discouraging other responses, but you may be interested in these

Keeping privates clean - general overview for Europe

I have a possibly prurient and somewhat unusual question about how certain sex acts have historically been perceived... - Rome; there are a few comments regarding hygiene

There are some good answers here, so I'll try to add to it as I can.

First off, the idea of modern hygiene being, well, 'modern,' is actually a myth; we have returned to a period in history when more regular bathing was the norm. Sure, there wasn't the fruity- or floral-scented soaps (anti-aging creams, retinol, and alpha-hydroxy acids) and it wasn't QUITE as common for individuals to bathe alone, but it was not unheard of in Europe before the Elizabethan period and has been relatively common in the rest of the world for a long time.

Take for instance Persians; bathing in Safavid Persia was relatively common, usually scenting your hair or beard with essential oils from flowers afterward - any man courting a woman would scent his beard and be generally as appealing to smell as he could be. There is a lot of rather ribald (given the social context) poetry which could indicate that oral sex was on the mind of at least a few poets. And it is not just in Persia either: a lot of the poetic motifs and styles were borrowed in this period from Indian texts which themselves harken back even older time periods, such as 4th c BCE's Kama Sutra. Nonetheless, all of these societies had some kind of regular bathing, but maybe not the bathing you're thinking of when you pour in some Mr. Bubbles on a Saturday night.

In Islam, the washing of the face, hands, feet, and (more often than not) head is common because you don't want to bring filth into the presence of God, so there's at least some modicum of hygiene even at the lowest levels. The higher up in social standing the more access to bathing you have (as well as the expectation to have bathed regularly), so that by the time you get to people who have time to write poetry for a living, their object of desire was most likely relatively clean, though probably not as obsessively clean as we are today.

Throughout Turkish history (at least until the 18th century or so), baths (or hamam) were often communal for the genders and consisted of steam rooms as well as different pools in which to bathe, each having different temperatures and functions. Sick and healthy, young and old would all use these baths; men in their baths, women in a different one (usually a different building all together). Friends or relatives would help you reach the spots you couldn't when washing or drying, or just sitting around sweating. There were also often masseuses employed in Turkish bath houses, which was ONE way to get clean as well as to work out the kinks of daily living. Bathing could be a daily activity, but was usually only every few days or weekly in the early modern period (say 16th to 18th century).

One thing I find interesting is that Crusaders brought bathing back to Europe in the 12th century. I know that London had bath houses similar to hamams all the way up to the 14th century. In the English context, at least, the bath houses were unisex; men & women used them together regularly and were often completely nude (well, except for most respectable women who kept their hair covered). A Woman could let their hair show, but this was usually a sign that she was for hire. Over time bathhouses became synonymous with bordellos - I think the latter grew out of the former - and were even licensed by the crown and sometimes run by the local Bishop. Unfortunately, a series of events and decisions (the miasma theory of disease, where to get clean bathing water in crowded London, and taxes on soap, for instance) shut those down in England, at least, right around the Tudor period. But the Tudors and others later on still wanted to be as clean as possible; they used linen undergarments to wick away sweat and grime and changed the undergarments daily. The whiter the garments, the more 'clean' you were (both physically and morally), and thus the more attractive you were.

But, if we fast-forward to 19th century, sex (especially oral) and cleanliness partnered up again; this time in France where the bidet was popularized by French courtesans and high-end prostitutes as a way to clean up in preparation for the next suitor/client. Presumably sex workers in other countries also liked to freshen up a bit around that time, but I'm not sure. I do know that by the time that we get to the 19th century in Turkey and Egypt, bathing was a relatively regular thing for the Middle Classes, especially those who were emulating the French and English elites they hob-nobbed with, so it is not unusual to come across a fairly old house or apartment building with pipes that are over 100 years old in Cairo; my apartment near midan al tahrir had lead pipes from the late 19th century in the bathroom, which kind of offered a double incentive not to let water splash in my mouth when I showered and to use bottled water to brush my teeth with, but I digress.

So, I guess the answer is a little more complex than you'd like, but three factors stand out; 1) people were not always as dirty as you'd think in pre-20th/21st century societies so it probably wasn't a big problem, 2) each society had certain standards of cleanliness and tolerated certain bodily odor smells because they themselves were probably a little (or a lot) stinky, and 3) there is at least a fairly strong link between sex and bathing, which might make one assume that yes, freshly clean naughty bits are much preferred (in many cases) to not-so-clean naughty bits.

Sources: Persian Love Poetry by Vesta Curtis Faces of Love: Hafez and the Poets of Shiraz ed by Dick Davis History Laid Bare by Richard Zacks

OPs question is premised on the assumption that individuals would have found it disgusting to perform oral sex in historical times when personal hygiene standards were lower. However, so long as the individuals engaging in oral sex were living up to the standards of the time, they may not have cared if it had been a while since their bits were cleaned.

So, is there any evidence that people in historical times wanted to live to a higher standard of personal hygiene but were precluded?