The nickname I've found offensive is "Jack" for anyone named John. I suspect it's presumed to be a "friendly corruption" for the French variant Jacques; but I always found it presumptuous when people tried to change my name, so once I matured a little I just never answered until they got it right. The ones who tried it before that mostly survived, but ... .

It was a matter of some significance within the family since:

My grandfather (John) was known as "Man." When his dad (John) died, and he took over running the horse farm at age 12, the neighbors needed a way to distinguish him from his dad, so some called him "the little man" for a time, and "Man" actually was a "real name" used occasionally in the community so it stuck, and he didn't object. (When a cousin bought a new car while in High School, the dealer forged grandpa's name as cosigner, but thought his name was Man and grand dad always used John on legal stuff.)

My dad (John) picked up a derivative of the last name due to a paucity distinct first names in his early school years, and it worked well enough for him that most people thought his real first name was something else.

I was given a "nickname" as a child that was used within the family, but never known by the outside world, and John has always been good enough elsewhere.

My son (John again - not my fault) was called by a middle name in the family, but now prefers just John. His refusal to include a middle initial for business purposes causes some confusion, but it's amazing - and rather stupid - that a majority of businesses don't allow for entry of an initial in their databases and apparently can't address mail with an included initial.

As a kid, two aunts were called "Peggy." One was named Ida and the other was Mary. My aunt Sylvia was called "Sib" by her husbband, and I never figured that one out; but he was the only one that used that name for her. Very few others within the family had "nicknames" that I ever heard of.

There often are reasons why people prefer the name they give you, and in my opinion using anything else is just "rude" unless you're both less than about 9 years old. One of the worst cases I've known was Harold who very strongly objected to being called "Harry." (It was well known that his middle name was Peter.)

John