Byrne is a dodgy, dodgy bastard.
There was the Superman/BigBarda porn movie thing in Adventures of Superman: was it a Darkseid henchman called Slugg or something? He has mind control over the two and is making them have sex and filming it. At one stage he commands them to get back on the job, so to speak, and Big Barda says something like, "No, please not again...". At the end of the story the bad guy is defeated, and we see a bemused Mister Miracle who must have been wondering what to do about the issue of his wife being forced to have sex with Superman. I think I was 20 or so when I read this and remember wondering what the hell small kids reading Superman would have made of this issue.
Then there was the She-Hulk adults-rated graphic novel. She-Hulk is nude, in chains, being tortured on the SHIELD helicarrier by rogue SHIELD agents. She busts loose, steals some clothes, and is shot in the chest, revealing large dark green nips under the shredded shirt. There's all sorts of icky Freudian skullduggery around Byrne letting loose over She-Hulk's breasts. You get the impression that Byrne is doing all this for his own dirty private amusement first, and as a paid job second.
Oh look there's more:
http://cbddossiers.blogspot.com.au/2006/09/record-john-byrne.html