Something Rather Significant
Disclaimer: I don't own HP. Getting tired of these things already.
Harry read as many books about what had happened to his parents as he could. Soon it was time to go to Hogwarts. Harry was so excited he could barely contain himself. Sirius, as was to be expected, overslept. Harry, convinced that trying to wake his dad would be dangerous, decided to bug Remus into getting the other man up. Remus, true to his nature, got so fed up he once again threatened to remove something rather significant from Sirius' anatomy if he didn't get up at once. Harry, now knowing what the 'something significant' was sniggered as Sirius hurried around getting ready.
Harry is like a Remus/Sirius mix. Environment over blood. Proven fact.