You’re hiding behind the shrubbery outside your former home as you watch your ex-wife have sex with some younger guy, and then the dog comes over and starts barking and you run for it. But if you’ve been busted by a dog you wouldn’t yell “heel!” as you run off because you wouldn’t want your ex to hear your voice. You’d run away as silently as possible. That’s why the scene isn’t funny. You have to do this kind of thing exactly right or it doesn’t work.
A similar scene happens in Paul Mazursky‘s Blume in Love when George Segal is snooping outside a therapist’s office and listening to his ex-wife, playing by Susan Anspach, share her thoughts. Anspach tells the therapist she’s sensing that Segal may be snooping outside; the therapist asks if she’d like him to check and she says yes. Cut to a shot of Segal running down the carpeted hallway as quickly as possible on the balls of his feet, anxious not to make a sound. That was funny.
I mentioned the Mazursky film because Stuck In Love obviously has the same ring and cadence. I’ll bet director-writer Josh Boone had it in mind at some point.
And by the way if that dog is one that you and your ex used to take care of together he’s not going to bark if he sees you outside the house. He’s going to come up and whimper and pant and want you to pet him. It’s even debatable if a strange dog is going to bark at you unless he’s an asshole, which admittedly some dogs are.