I try not to do it but I understand that it is easier to spot the job of someone than their name (especially for 4-man duties). Thus, I do not get offended when I am called whm or healer (or whatever I am playing).
However, I remember back in 2.1 when Pharos Sirius was people's nightmare and we just got it, someone said right away "Does our healer know at least what to do?" and I got offended first because it was a 3rd person question and second because it is not that hard to read what Siren's debuff does on first try <__<".