Some Anvils Need to Be Dropped: Mary's general attitude comes down to be unafraid to do this. In "The Blacksmith's Tale" for instance we find out that the main reason Mickey Finn came to Earth was because he figured that by the time he'd need maintenance after escaping his masters we'd be at a technology level capable of supplying what he needed. The regulars are down in the mouth that he didn't do it out of love for our species and our finer qualities, but Mary tells them they're dumb for expecting this of someone to whom we're at basically the level of chimpanzees.
Squick: Erin, who's at the physical age of one years old but has had the entire Internet downloaded into her brain, goes around lining up future sexual partners for when she's 16. She's actually heard to utter the words, "I'm going to start fucking when I'm sixteen, would you like to take a number? I can work you into the single digits if you hurry."
Ralph, a talking German Shepherd, occasionally has sex with human women.
Though considering how much more intelligent than any female dogs he's likely to encounter, wouldn't sex with a non-verbal animal be as Squick-inducing as someone having sex with a person who has severe mental retardation, or otherwise may not be able to give informed consent?
Except that he also has sex with female dogs.
The regulars at Callahan's are an open bunch, but Spider kind of has this thing about just mentioning characters' sex lives that can seem a little too open. Like in Callahan's Con where Jake describes a merman who's barely in the book, then just out of the blue says "he doesn't have a tail, but he gets a lot of it." Also, Nikola Tesla appears in two of the books and in describing him, both times it's pointed out very clearly that he was NOT a virgin at the time of his "death." That sorta kinda fit in the spinoff set in the bordello run by Callahan's wife, but it still seems like a really weird thing to just toss out there.