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!
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.