Nicknames can be hilarious, savage, apt or devastating.

Whenever a pupil is referred to by a nickname, I always ask the pupil if they like being called Snowy, or Babyface, or whatever.  Since nicknames are almost always chosen by others, it is best to check with the bearer of this sobriquet if they are happy with it or not.

Young people are particularly good at hitting their target when it comes to bestowing a nickname on a teacher.  I was taught at secondary school by a maths' teacher who was called Neuter Gender by the boys.  When this curiously colourless, straight-laced man heard his nickname, he had a breakdown.
Conversely, some teachers relish their nicknames, as much as Margaret Thatcher did when she heard that she'd been called The Iron Lady.  Again, I had a teacher we called Ming the Merciless (after the grim villain in Flash Gordon comics). He referred to himself in class as Ming. We were both amused by this and also annoyed that he knew and delighted in his nickname.

Some nicknames can be therapeutic.  As I have mentioned in a previous post, when I discovered that the pupils called me Volcano, it was a warning to calm down.  And the more I relaxed, the better a teacher I became and lessons became more enjoyable.

Sometimes nicknames virtually become the person's name.  I have a friend I call Snake, and to this day I don't know his real name.  I might have known, a long time ago, but now he will forever be Snake.