Thats your approach which is fine. But OP made it clear theyd be more comfortable if they just had an easy excuse that doesnt raise eyebrows. OP shouldnt have to explain themselves, but not everyone is comfortable with that.Id go with hernia.Is there a reason why you have to give the info in the first place?"I'm on alternate duties for medical reasons" should be more than enough for anyone who isn't your doctor. Honestly "I'm on alternate duties" with no further details whatsoever is a complete sentence already.You can say hernia repair if you want, not saying you can't, but it's a bit bizarre to me that you've been put in a position where you feel like you have to reveal more than you wanted to or make something up just for an ice breaker with Carol from Accounting. An ice breaker should be, like, "what tv shows are you watching recently" or "what's your favourite meal"! Not "please explain something potentially very personal".
Dont tell them you are getting circumcised. Medical co-workers can be the worst.