Is calling someone a Paki racist?
Spoiler Alert. Yes. ffs.
If someone is racist to you, I don't much mind that you don't care.
That one person doesn't find being abused racially offensive has no bearing on how "some of them" feel.
Let me be clear, racism costs, you'd don't want to collect that's fine, don't expect anyone else to turn the other cheek. I would encourage the expectation of prosecution and prolonged violent retribution.
Ask someone a little older than you why that kind of language fell out of fashion, you'll know who to ask by the prominent facial scarring.