Reminds me of a night watch at Denver Center. During a phase called 'DARC Only' (means limited computer processing during scheduled upgrades, and subsequently does not have error alert) 3:00 A.M., two aircraft at 41,000 feet, opposite direction come within a mile of each other. (Minimum separation requirement is 5 miles.)
United pilot: "Hey center, how close was that aircraft that just passed off our left?"
Controller: "5 miles"
Pilot, after a bit of hesitation: "Nice tie!"
