I would never call anyone a noob and think it's just stupid when I see others do it. The only reason people noob-call is because they don't have it or cannot kill you because of it. If you choose not to have a defence level, or choose not to use prayer, that is your own fault. You cannot blame anyone but yourself for that. There are no rules when you PK, so players can do whatever they like, and if that includes potting/praying/using defence, then so be it.