This is especially hilarious^W demoralizing when the same company continues to actively recruit across all available channels. Successive waves of aggressive recruiter spam from some of my past "dead silence" rejections continue to cause hilarity^W^W rub salt on the wound to this day.
Respond with "I'd love to start a conversation about this great opportunity, but I'm still waiting to hear back from you about the interview we did 6 months ago!" :-)