Mademoiselle is a French loanword meaning "Miss" or "young lady." While not strictly German, its inclusion in a German song adds a touch of international flair and a slightly more formal, yet playful, address than a typical German equivalent.
In the context of "Party im Hotel," the singer uses it to address a woman, asking, "Sag mir, Mademoiselle, wieso schaust du mich so an?" (Tell me, Miss, why are you looking at me like that?). It's an intriguing choice that stands out and hints at a certain sophistication or flirtation within the party setting.
This song is about throwing everything into one wild night at a hotel party and refusing to think past it.
The singer wants to stay up with someone until morning and stop worrying about anything bigger, like what the world outside is doing. Money comes up a lot, but mostly to be waved off: burning through a fortune doesn't actually make anyone happy, and status symbols like chains and fur matter less than just being there with her.
Underneath the bragging there's some honesty too. The singer admits that not everything is as perfect as it looks, that it's hard to tell what's real from what's just for show, and that he's often had enough of the world. Still, none of that stops the party.