Seems Mario's not such a suave, gracious gentleman after all. He's been having a go at Lisa for cleaning up too much. Not because he thinks she's worth more than that, or because he's bothered about the others being dirty, lazy sods... but because he doesn't want her to be more popular than him.
And let's make this one 'quote of the week' while we're at it: "Throw a few spanners in the works, it's too nice, too happy happy... Otherwise, before we know it, I'll be gone and you'll still be here." In the words of the Bard (credit where it's due, right?): "Aye. There's the rub."