That's frustrating.
There's a little Yorkie that frequents the dog park that can't be more than 4lbs. He's so obnoxious, he's constantly humping other dogs, and he will pick one dog and just follow them around the park the entire time. Well, once he picked Jackson. Jackson is so laid back, he didn't care for a while, the little guy was practically humping his leg as Jackson was running... he would NOT leave him alone. I could tell Jackson was getting really irritated so we just left.
But what irritates me the most is the owner says "oh that's how he plays! he's so small, it's the only way he knows how to!"
Yet, she won't neuter him, says she is going to breed him (he is not a standard Yorkie and has a terrible temperament) and if any dog tries to hump him... she (and he) gets mad.
I'm very understanding... I totally get that dogs will be dogs. It's when the owner just sits back and laughs and thinks it's no big deal and doesn't even attempt anything and it's happening repeatedly. It's very frustrating.