Cat Scratch Disease: This is a common condition caused by Bartonella henselae, transmitted through cat scratches or bites. It often presents with lymphadenopathy, particularly in the axillary or groin regions, without other significant symptoms, making it a plausible explanation for the intermittent nature of the lymphadenopathy in a young male.

Infectious Mononucleosis: Caused by Epstein-Barr virus (EBV), it can lead to lymphadenopathy, although it typically presents with fever, sore throat, and fatigue. The absence of other symptoms in this case does not rule it out entirely, as presentations can vary.
Toxoplasmosis: An infection caused by Toxoplasma gondii, which can result in lymphadenopathy. It's often asymptomatic but can cause lymph node enlargement, particularly in the absence of other systemic symptoms.
Tuberculosis (TB): Although less common in young, otherwise healthy males without exposure history, TB can cause lymphadenopathy. The intermittent nature and lack of systemic symptoms make it less likely but still a consideration.

Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present with lymphadenopathy. Although less common and typically associated with other symptoms like weight loss, fever, or night sweats, the potential severity of missing this diagnosis warrants its inclusion.
HIV Infection: Acute HIV infection can cause lymphadenopathy among other symptoms, but some individuals may remain asymptomatic or have very mild symptoms. Given the potential long-term consequences, it's crucial not to miss this diagnosis.
Syphilis: Particularly in its secondary stage, syphilis can cause lymphadenopathy. The disease's potential for serious complications if left untreated makes it a "do not miss" diagnosis.

Castleman Disease: A rare disorder that involves an overgrowth of cells in the lymphatic system, which can cause lymphadenopathy. It's less common and typically presents with systemic symptoms, but the unicentric form might be asymptomatic aside from lymph node enlargement.
Kikuchi-Fujimoto Disease: A rare, self-limiting condition that causes lymphadenopathy, typically in the cervical region but can involve other areas. It's more common in young women but can occur in men.
Rosai-Dorfman Disease: A rare histiocytic disorder that can cause lymphadenopathy, often without other significant symptoms. It's a diagnosis of exclusion and might be considered if other tests are negative and lymphadenopathy persists.