Simply put "life-size-body" in positive.
I tested it on very high resolutions up to 1280x1024 and "overexcited-having-fun" together with "crazy-flexible-pose" and the result was always a perfect body. Not even the slightest deformation.
And to see if it has its limits, i tested it with children, since most of the time, small bodies are the hardest on every checkpoint. And it still worked. Even after i left my negative-prompts blank.
BUT! If you wanna use this prompt, i highly recommend to prompt chlothes, too, since checkpoints, the second they read "body", end up generating naked bodies.
And here the second part, that happened during testing:
If you put "flexible-deformities:2" in negative, it completely stops any deformation instantly. Well, this idea popped up, because of "crazy-flexible-pose". and after i added a theme-park-scenery, that "overexcited-having-fun" ended in a crazy mix of limbs suddenly.
UPDATE: some realistic checkpoints mistake this prompts for some kind of doll and generate "life-size-dolls". if this happens to you too, simply put "real-person" in positive and "doll-like-body" in negative and it will work again like its supposed to.
UPDATE 2: since a user had problems getting this prompt to work with furries, i got it to work properly after adding "furry-character" in positive BUT i had a hard time getting proper hands and feet most of the time. "flexible-deformities" did not work on every checkpoint using furries, so i had to make a new prompt that doesn't mix up human and furry and generate only human-similar-hands. Put this in negative: "physically-shameful-inhuman-joints:2"
This prompt, to be honest, is just something that i quickly made to get to the point. I won't publish it as a single prompt, because, even for me, this prompt looks just "shameful" :D