“鸽” means “pigeon,” and “了” is a marker for perfect tense. This term, coined by Chinese netizens, derives from another colloquial saying “放鸽子” (fànggēzi, literal meaning: fly a pigeon), which actually means “to stand someone up.” Therefore, this term is used when someone fails to keep an appointment or to do something as they promised.
Zuótiān de yuēhuì zěnmeyàng？
How was your date yesterday?
Wǒ hǎobùróngyì yuēdào xiàohuā kàn diànyǐng，jiéguǒ tā gēle。
I finally got the campus belle to agree to go on a movie date with me, but she stood me up.