Royal Pain Lyrics
Not a lot, just a little bit
Someone's always tryin' to keep me from it
It's a cryin' shame
It's a royal pain in the neck
I'm just tryin' to get by
With my pride a little bit intact
Ask me any question and I'll level with you
I didn't ask but anything but bein' with you
That's the only thing I was born to do
And they're all insane
Such a royal pain in the neck
I'm just tryin' to get by
With my pride a little bit intact
Another day is put to the test
Lord knows I'm doin' my best
Never a brother, always a guest
It's a cryin' shame
It's a royal pain in the neck
I'm just tryin' to get by
With my pride a little bit intact
And they're all insane
Such a royal pain in the neck
I'm just tryin' to get by
With my pride just a little bit intact

The first line is obviously a reference to I need some sleep wich appeared on Shrek 2 and this one appears on Shrek 3

Yes, it's a tidy little tie-in back to "I Need Some Sleep" from Shrek 2.
It's supposed to be written from the perspective of Mr. Shrek himself, finding himself as part of aristocracy, and not yet comfortable with the role and the society he's forced to keep now - "Royal Pain,.. they're all insane". "Never a brother, always a guest" - he hasn't yet found acceptance, or comfort, in this new role. And yet he does it because of his love for Fiona (i.e. Ask me any question and I"ll level with you. I didn't ask for anything but being with you. That's the only thing I was born to do). All the while yearning for the simplicity of his/their former life.
Ties in wonderfully with the opening scenes of the movie.