The only reason these offensive words are offensive is because people give that meaning to them, for example by reprimanding those who use them, or banning the words. I might use the term Jap or Japs, not because I hate the Japanese, because it's quicker than typing 'Japanese People' or 'Japanese Person'. The words 'Yank' and 'Jock' are similar, and I've never seen any posts removed for the use of those words. 'Paki' is different because it's often used to refer to all people who look middle Eastern, but from what I've heard, it is fairly normal for Pakistanis to use it between themselves.