I must confess this has never bothered me and it has never even occurred to me that it might bother someone else.

I would find someone calling me by an abbreviated version of my name without my authorisation to be far more offensive.

It's the equivalent of

A: "What's your name, son?"
B: "David Smith"
A: "Well, Dave - do you mind if I call you Dave?"
B: "Well..."
A: "Great! Well, Davey.."
B: "Davey?"
A: "D-Dog! the Davester!"

etc etc.

It's just a lot easier in the middle of a DF run to call out a job role. It has a three letter abbreviation that is understood by everyone in the party, it's even in autotranslate. WAR{tab} is a lot faster to type out than "O'Hizgledred Binglybop". If you are offended, fine, that's your right. But the person hasn't done anything unreasonable or rude.