The disappointment experienced at the moment you inspect or experience something, a fter having saved its inspection for just the right time, only to find it's not what you'd hoped for. Example: I finally got up the nerve to ask her out, and when she smiled, I discovered she had bad teeth. It was another lunchbag letdown.
LUNCHBAG LETDOWN
Meaning of LUNCHBAG LETDOWN in English
Slang English vocab. Английский сленговый словарь. 2012