with $rand and if statements it will be long script you can create txt file and fill it with bunch of messages like

randommsg.txt

Code:
hey!
hello!
welcomeback
howdy


then use this code:

Code:
on *:text:hello:#: {
  if ($nick == YOURNICK) { return }
  ; this will pick random line from "randommsg.txt" and use that
  msg # $read(randommsg.txt) 
}