Once I knew a guy who had flown F-15s then was picked to fly the F-16 with the T-birds. After his T-bird tour, he went on to fly with a frontline F-16 unit.
His callsign became THOC, which stood for “Thousand Hours, Zero Credibility.”
To his credit, he took it lightly, and eventually became a very good Viper driver.
THOC? Ouch!