If you leave quickly enough, you can just decline to mention the job, if you like; you're not obligated to give anyone a complete accounting of your work history, and nobody will care about a few months' gap between jobs.
It's also likely not going to be as big a deal as you think to explain that "the position turned out to be a bad fit", so long as you can talk about why that was, in a neutral, professional way which demonstrates that you are a reasonable person who knows what a good fit would look like.
As for "spin," something like learning what you dislike in a position or company, or how your current position has reinforced your passion for the position you're applying to - things with intent between the lines are fine. Avoid saying anything like "I needed the money" or "that place sucks so bad."
Above all, learn from this (of course). Was anything weird during the interview and hiring process that you can see in retrospect was suspicious or misleading? If they had said one extra sentence in the job description, would it have tipped you off that the role was a bad fit? Is it really the job or is it the people that are a bad fit?
Not that you'd want to talk up any of those in a future interview...but there are often ways to allude / hint / talk between the lines. And obviously you want to be sure that you don't repeat the mistake.
(One of my three major regrets in life that I did not.)