I was not shy about going for hair transplant so I had no qualms telling anyone who sees my transplanted hair or the donor stitches/scar.
However there are some individuals that I do not wish to tell, so if these people ever ask, here's what I will say:
Transplanted Hair: "Oh... as you know, I was in Thailand for a week. I became a novice monk, it's a common custom in Thailand. So as a gesture, they shaved a little off my hair. It was tough man, no beer and sex for a week! But it was great for some inner reflection...."
Stitches/Scar: "Oh I was just having a drink at (name of your fav pub). Was minding my own business when a beautiful lady chatted me up. After a while she wanted to bring me home but I refused, telling her that I'm married/tired/not in the mood. She didn't take kindly to that so I learned the hard way not to refuse a frustrated woman...."
Hope these excuses will come in useful for you one day!
Disclaimer: Use at your own risk!