Sinister clasped his hands behind his back and looked at his son. He waited a heartbeat, letting the silence stand before replying in a completely detached and emotionless tone, "The tissue is delicate and it is far easier to reopen and infect without proper cleaning and examination. Something you cannot do for yourself."
He allowed a moment for that to sink, then continued, "Have I been inappropriate in my methods? Have I made any unwanted sexual overtures while caring for you? No to both. What is it that makes you feel uncomfortable in allowing me to ensure your continued health."
If they had to have this discussion every time and stretch this out, they would. Sinister was not going to let his son win an argument where his health was concerned. He would force himself to be patient with the boy and not force the inevitable.