Despite what people say, it's really not a short version of Pakistani, like Brit.
Paki is a racist term used since the 60s to offend anyone south asian. It can be viewed to be as bad as the n-word, and you wouldn't use that, would you?
I'm Sri Lankan and if someone called me this word, I would find it so offensive, I'd probably cry. And I don't cry a lot.
Guys? Don't be racist. We're all humans, we're all the same on the inside, so focus your hate on the things that deserve it, like murder and child abuse.
NB: please don't do the "but if Pakistani people call each other "paki", why can't we say it?" It's not the same. Black guys call each other the n-word. Does that make it okay for other people to use it on them?
"So what if I called you a Paki, it's just a short version of Pakistani!"
"You're an idiot.