Don't answer. Don't listen. Don't help. Don't play with them until they can produce a line in RP. Don't reply to them in system if you have to, take it to private. More disheartening than having a bunch of new people saying random unmarked stuff in system chat, is having older players, who should know better, breaking RP to reply to the idiocy.
"Do not argue with an idiot. Other people may find it difficult to tell who the idiot really is."
Instruct and warn them. If they keep willingly harassing people, just report them.