Diabetic neuropathy: Given the patient's history of diabetes, diabetic neuropathy is a common complication that can cause penile pain due to nerve damage. The patient's long-standing diabetes increases the likelihood of this condition.

Erectile dysfunction-related pain: Patients with a history of CABG and diabetes are at increased risk for erectile dysfunction (ED), which can cause penile pain during or after erection.
Urinary tract infection (UTI) or prostatitis: Diabetic patients are more prone to UTIs, which can cause penile pain, especially if the infection involves the prostate (prostatitis).
Peyronie's disease: This condition, characterized by the formation of scar tissue in the penis, can cause painful erections and is more common in patients with vascular risk factors, such as those who have undergone CABG.

Penile fracture: Although less common, a penile fracture is a medical emergency that requires immediate attention. It typically occurs during sexual activity and can cause severe pain.
Priapism: This condition involves a prolonged erection that is not related to sexual desire or stimulation and can cause significant penile pain. It is a medical emergency, especially if it lasts more than four hours.
Acute coronary syndrome: Given the patient's history of CABG, any new onset of pain should prompt consideration of cardiac causes, including acute coronary syndrome, although penile pain is not a typical presentation.

Penile cancer: Although rare, penile cancer can cause penile pain and should be considered, especially in diabetic patients or those with a history of poor genital hygiene.
Sickle cell disease crisis: In patients with sickle cell disease, a crisis can cause penile pain due to vaso-occlusive episodes affecting the penis.
Fabry disease: This rare genetic disorder can cause neuropathic pain, including penile pain, due to the accumulation of a particular type of fat in the body's cells.