When I was a kid, I would just take them literally and get frustrated. Like when people would always say to me, “what’s the matter, cat got your tongue?” I would get really mad and say “no!! !” (thinking, my tongue is right where it’s supposed to be, idiot). It’s only after I’d heard the expression a hundred thousand times that I even really tried to decipher it’s meaning. Then, of course, the thought of a cat actually having my tongue at all just seemed so ridiculously absurd, that I’d still get angry whenever someone said it to me.
Some common metaphorical expressions just don’t make a lot of sense to me. Like I can understand that it’s “just an expression”, or whatever, but they still bug me because sometimes I just don’t see the sense in them. Take these two expressions: “slacking off” – I can make perfect sense of this because it implies exactly what it means. Being “slack” means the opposite of working. But “dogging it” also tends to be a popular term, that means the same thing. Where did that come from? Is it meant to imply that the person is as lazy as a dog? Well, not ALL dogs are lazy… Or does it mean something else?
Where I live, people use the term “dogging it” quite differently, although it still means “slacking off”: Not long after I moved here and started my new job, I was sitting at my desk late one quiet afternoon when one of my co-workers wandered by and announced quite matter-of-factly that she thought it was “time to f*ck the dog”. I stared at her for a second, wondering if she was going to tell me something about her dog – I knew she had one – that maybe this was just a funny way of saying he’d done something bad and she was going to punish him somehow. I waited for her to continue, but instead she heaved a restless sigh and wandered back to her own desk, leaving me even more confused. Over the course of the next few months, as I slowly became more familiar with some of the regional slang, I figured out that “f*cking the dog” was just a more vulgar variation of “dogging it”. Also acceptable are “pounding puppies”, and the ever popular, “screwing the pooch”. Sure, it sounds funny, but I'm not sure what exactly beastiality has to do with not working.

Screwing the pooch can be applied to mean either "I just messed up really badly and now I'm in a whole lot of trouble" or the "being lazy to one's detriment" idea you mentioned.