I never, ever thought I'd have to say this.(warning solitary scrabble mentioned)

[Bibliophile]

Just wondering, but was there really a need to post a warning about a dog humping?  I mean, it's a dog.  I understand a bit of warning for scrabble topics that are a bit more informative, but it's a dog...     It just makes me giggle every time I see the thread topic.

Yeah, I also think this is a case where what the dog is actually doing changes the advice (I'm *still* not sure if it's scooting or masturbating or licking or...what) so I think just spelling it out might make the most sense here. 

Is it bad to say the dog was humping something on the ground?  Dogs do that.  And I don't think a warning about a dog was actually necessary. 

[Amava]

Yeah I don't think it's offensive at all to speak of these kinds of dog actions; nor does it squick me out when a dog does that in front of me.
However if I was at someone's house and they asked me to stop my dog from doing something they disliked, I would do so.  I think your ex is being inconsiderate and deliberately unpleasant towards you; and you don't have to accept that.

Anyway I agree, firstly, with the people who suggested that the dog might just be itching (and not in a sexual, pleasant manner) and that there might be an underlying medical issue; and secondly with the people who said that it would be perfectly within bounds for you to address the dog directly when he does that at your house, and redirect him in a friendly manner. If you want to "choose your battles wisely", leave the ex out of it and speak to the dog: he probably listens better to you than your ex does. 

[Starchasm]

I'm totally confused about what the dog was doing.  Was he just licking himself and scooting, or was he actually humping something?  None of those things are necessarily sexual in nature, but I understand why humping makes people uncomfortable (even though it's totally normal PLAY behavior).   If he was doing the "boot scoot" as we call it in my house, then it could be anal glands, constipation, or worms and I'd suggest a vet.

Nonetheless, I think you would be perfectly within your rights to make the dog stop doing whatever it is that annoys you at your house.  I don't think you were required to go through your ex as middle man, and think there probably would have been less drama if you'd just said, "Sparky, stop it!" instead of "Bob!  Make him stop! What do you mean you think it's funny?  Make him stop!"

[Twik]

I think you have two problems.

One, the dog needs to see a vet. "Scooting" is normally trying to relieve a pain or irritation, not getting a thrill.

Second, you are still hanging out with an ex who doesn't respect you. Why are you trying to "pick your battles" rather than cutting ties?

[delphinium]

And if the dog isn't neutered, it's something your ex might want to check into.  Makes a better pet.

[WillyNilly]

The problem here, as many have already pointed out, has little to do with the dog itself, and much to do with the ex-boyfriend how he treats you/listens to you/respects your home.  He's an ex for a reason and perhaps you need a bit of distance from him.  I don't know your details, etc, but I have personally found, and through witnessing and speaking to friends found, while yes friendships among ex's can happen, its actually best if there are two things that happen:

1. Total separation for a period.  Unfriend on Facebook, delete old texts and emails, take his phone number out of your phone, and have zero contact for 3-6+ months.  It might mean turning down parties for a while, and avoiding clubs or other common interests, but its good to expand to different social circles and different activities.

2. When you re-establish friendship, maintain healthy boundaries and don't fall into old patterns.  Having done step 1 this is easier, because you now have expanded and grown socially and emotionally, so you can set new friend relationship expectations and behaviors.

[Wordgeek]

Insofar as this is an actual etiquette issue, the matter has been dealt with and you've received appropriate advice.