Apologies- this has definitely come up in a thread here before and I did my best at trying to find it through various searches/search engines. If someone wants to link the thread if they can remember it I'd be more than satisfied. Anyhow, essentially one of the Historians here was discussing Roman sexuality and stated that the act of cunnilingus was extremely taboo. That historian then provided a quote that I am trying to recollect that went something like 'If even cunnilingus doesn't make so and so blush nothing will.'
All that comes to mind at the moment is a quote from Martial's Epigrams, in which he is making fun of an extremely pale man who can't seem to gain some colour: he exercises, sits in the sun but to no avail. Martial finishes his tirade by saying that the man performs oral sex but is still ghost-white.
Edit: Found another post that explains this much better.