Varicose Vein: This is the most likely diagnosis given the description of the lump as squishy and the mention of a possible varicose vein. Varicose veins are common and can present as soft, bulging veins under the skin.

Lipoma: A lipoma is a benign tumor made up of fat tissue and can feel soft and squishy. It's a common cause of lumps under the skin.
Cyst: A cyst is a fluid-filled sac that can develop under the skin and may feel squishy. It can be caused by a variety of factors, including blocked oil glands or infection.
Hematoma: A hematoma is a collection of blood outside of blood vessels, which can cause a lump. It might feel squishy, especially if it's not fully clotted.

Deep Vein Thrombosis (DVT): Although DVT typically presents with pain and swelling, it's crucial not to miss this diagnosis due to the risk of pulmonary embolism. A lump could potentially be a sign of a clot in a superficial vein, but it's less common for DVT to present as a distinct "lump."
Soft Tissue Sarcoma: While rare, soft tissue sarcomas can present as a lump under the skin. They are malignant tumors that arise from the soft tissues, including fat, muscle, and blood vessels.

Lymphangioma: A lymphangioma is a rare, benign growth that consists of abnormal lymphatic vessels. It can present as a soft, squishy mass under the skin.
Angiomyxoma: This is a rare, benign tumor that consists of blood vessels and soft tissue. It can feel soft and squishy.
Kaposi's Sarcoma: A type of cancer that can cause lesions or lumps under the skin, often associated with immune system dysfunction, such as in HIV/AIDS patients.