fair enough.
Actually, what you're supposed to do is not reply at all if someone is posting on old threads unnecessarily (http://tpt.io/.6759 number 11). Otherwise you're making the problem worse by bumping the thread some more. Ignore it and let a moderator deal with it if it's a genuine necro (by giving the user a warning, banning them, or locking the thread).
Why do all my threads turn into arguments about necros?