An idiomatic expression that describes disloyal people or behavior, that is, those who change sides or become disloyal at the first sign of trouble or testing times.

Example: “when the firm started getting into financial difficulties, some of its staff members resigned and left, just like rats leaving a sinking ship. At good times, the firm always provided job security and growth potential, and it would be inconceivable to see employees leaving it at a time it needed their support the most.”