The idiom "放鸽子 (fàng gēzi)" literally means "to release a pigeon." It originates from pigeon racing, where releasing a pigeon signifies sending it away. Over time, the phrase evolved to mean not showing up for an appointment, akin to letting a pigeon fly away instead of keeping a commitment.
For example:
Tā yòu fàng gē zi le, zhēn shi ràng rén shī wàng.
他又放鸽子了,真是让人失望。
He stood me up again, which is really disappointing.