Pelvic Floor Dysfunction: This condition is characterized by the inability of the pelvic floor muscles to function properly, leading to a range of symptoms including hard flaccid syndrome, post void dribbling, and constipation. The fluctuating nature of hard flaccid syndrome and the resolution of constipation could be indicative of variable pelvic floor muscle tone and coordination.

Benign Prostatic Hyperplasia (BPH): BPH can cause urinary symptoms such as post void dribbling due to bladder outlet obstruction. Hard flaccid syndrome could be related to pelvic floor muscle dysfunction secondary to BPH.
Overactive Bladder: This condition can lead to urinary urgency, frequency, and incontinence, which might be associated with post void dribbling. Hard flaccid syndrome could be a separate but related issue due to pelvic floor muscle overactivity.
Neurogenic Bladder: Neurological disorders affecting bladder control can result in a variety of urinary symptoms, including post void dribbling and hard flaccid syndrome, depending on the type of neurogenic bladder (e.g., underactive or overactive).

Prostate Cancer: Although less likely, prostate cancer can cause urinary symptoms similar to BPH, including post void dribbling. It's crucial to rule out cancer due to its significant implications for treatment and prognosis.
Spinal Cord Injury or Disease: Conditions affecting the spinal cord, such as spinal cord injury, multiple sclerosis, or spinal stenosis, can lead to neurogenic bladder and pelvic floor dysfunction, presenting with hard flaccid syndrome and post void dribbling.
Cauda Equina Syndrome: A serious condition where the nerves in the spinal canal are compressed, leading to neurological symptoms including bladder and bowel dysfunction. Early diagnosis is critical to prevent permanent damage.

Peyronie's Disease: A condition characterized by the development of fibrous scar tissue inside the penis, leading to curved, painful erections. While it could potentially contribute to hard flaccid syndrome, it's less directly related to post void dribbling and constipation.
Diabetic Neuropathy: Diabetes can cause nerve damage leading to a variety of symptoms, including bladder dysfunction. However, the direct link to hard flaccid syndrome and the specific combination of symptoms presented makes this a less likely but not impossible diagnosis.
Amyloidosis: A rare condition involving the deposition of abnormal proteins (amyloid) in various tissues, which can affect any organ, including the bladder and pelvic floor, leading to dysfunction. However, this would be an uncommon cause of the symptoms described.