The ‘birthday present’ is shorthand, used to describe a particular song that carries certain notoriety for an artist or group. This song has come to define the band/artist, regardless of its age, quality or potential embarrassment. When performing live, this particular track is virtually expected; failure to perform the number will lead to grave disappointment or even bitterness from the crowd.
The ‘birthday present’ obtains its name through its special gift-like quality that, if not received, tends to cause resentment.
If Led Zeppelin came to town they’d just *have* to perform ‘Stairway to Heaven’, it’s their birthday present!
When you have to pee in a movie but don’t want to miss anything, and must do the following mental equation: will the amount I have to pee cause enough discomfort to diminish my attention capacity for the remainder of the movie to an extent which is greater than the amount of the movie I would miss by making a mad dash to the restroom.
I saw Satantango last night, wonderful film but by the 5th hour I had to start doing pee calculus.