I was born with two Y chromosomes, AMA
I am a 26 yo man and I was just diagnosed with 47,XYY "syndrome" (also known somewhat incorrectly as Jacobs syndrome or "supermale" syndrome), in quotes since it can be close to asymptomatic and usually not debilitating. Of course, it results from an extra copy of the Y chromosome and it was caused by an error in sperm development.
I have inherited several physical and mental anomalies as a consequence, some unpleasant, most just curious. The most evident is that I am very tall at ~ 205 cm (6'9''). This condition is underdiagnosed and poorly understood so as far as I understand there's a lot of controversy over which symptoms are really linked to the illness and what their incidence is. I suddenly realised I had a match with enough of them to warrant pestering my doc for a karyotype analysis, and here we are.
Proof. That's all I have. I could also provide photographic proof of any physical symptom if requested, but as I anticipated by itself each singular symptom is not particularly impressive nor a smoking gun for double Y.
Ask me anything you might want about my experience. I understand there could be questions about sexual development or sexuality and I am comfortable answering, but let's be medical so I can keep this thread sfw.
EDIT: I know it might sound really otrageous, but I will not reply to private requests to see my genitals. I know, I know, what a prude.