What's that tune that Paris Hilton and Nicole Richie sing on the bus?

I walked in on the cat watching this a couple of times, towards the beginning of this show. Paris and Nicole were at the front of the bus, when out of the blue, they break into this piece that sounds familiar, but I can’t quite put my finger on it. Something like:

*Dah-dah-Daaaaaaaaaaaaah! Dah-dah-Daaaaaaaaaaaaah. Dah-dah-Daaaaaaaaaaaah! Dah-dah-dah-Daaaaaaaaaaaaah!
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You’d really have to hear it to know what I was talking about. Anyway, like I say, it does sound familiar—any guesses?