Type 2 Diabetes Mellitus: This is the most likely diagnosis given the patient's obesity and significantly elevated A1C level of 11.5. Obesity is a major risk factor for type 2 diabetes, and an A1C level above 6.5 is diagnostic for diabetes.

Uncontrolled Type 1 Diabetes: Although less common than type 2 diabetes in adults, especially in obese individuals, type 1 diabetes can occur at any age and would need to be considered, especially if the patient has other symptoms such as significant weight loss despite obesity, polyuria, and polydipsia.
Latent Autoimmune Diabetes in Adults (LADA): This form of diabetes has characteristics of both type 1 and type 2 diabetes and can present in adults, often with a slower progression than type 1 diabetes but may require insulin therapy sooner than type 2 diabetes.
Steroid-Induced Diabetes: If the patient is on steroid therapy, this could be a contributing factor to his elevated A1C, as steroids can increase blood glucose levels.
Cushing's Syndrome: A rare endocrine disorder caused by excess cortisol, which can lead to insulin resistance and elevated blood glucose levels, along with other symptoms like weight gain, particularly in the central part of the body.

Pancreatic Cancer: Although rare, pancreatic cancer can cause diabetes due to the destruction of pancreatic tissue. Given the significant elevation in A1C, it's crucial to consider this, especially if there are other symptoms like unexplained weight loss or abdominal pain.
Hemochromatosis: A genetic disorder that leads to iron overload, which can damage the pancreas and lead to diabetes. It's essential to consider this diagnosis due to its potential for serious complications if left untreated.
Polycystic Ovary Syndrome (PCOS) in a Female Partner (if applicable): While the patient is male, if there's a female partner with similar concerns, PCOS should be considered as it's associated with insulin resistance and diabetes.

MODY (Maturity-Onset Diabetes of the Young): A rare form of diabetes caused by genetic mutations that affect insulin production. It typically presents at a young age but could be considered in adults, especially if there's a family history.
Wolfram Syndrome: A rare genetic disorder that can cause diabetes, among other symptoms like blindness and deafness, due to the degeneration of the pancreas and other organs.
Klinefelter Syndrome: A genetic condition in males that can lead to insulin resistance and diabetes, among other symptoms like infertility and developmental delays.