A frustrating situation when after feeding a guy booze and listening to him talk about himself all night at the bar, you get him home and as you take off his pants you're dissapointed to find that he has a teeny tiny penis.
Steve: "I thought I'd picked up a good fuck for the night then I suffered Lunchbox Letdown."
A lunchbag letdown occurs when something you had been looking forward to turns out to be far worse than originally anticipated.
The term originates in the lunchroom (be it school or office or otherwise) where after a long hard day someone sits down with their lunchbag hoping for something tasty. Instead they find something unappetizing, whether it be the wrong lunch, it's moldy, it's cold, or any other multitude of problems.
After such a situation, it can be said that your lunchbag was indeed a let down.
What will happen when obama's supporters discover he can't deliver what they expected. The rest of the world doen't give a rats ass about obama and isn't going to do his biding. He won't be able to bullshit down the price of gas, or bullshit up the value of the dollar, or the terrorist into changing their ways. They will kick his ass and send him home crying to his white grandma.