Regardless of your own discernments, if say Japanese people don't like being called Japs then don't do it. Similarly, if you have a nickname you don't like, you expect people not to call you by that n ...
I have made that mistake long ago but since then I use Jp for shorthand. But I must say, to lash out as someone for using it may make you both guilty of ignorance. Not everyone is aware of the derogat ...