In a way, a high-five is a a congratulation, so the guy in this music is kinda saying "viva a (nossa) vida de escória social/de vagabundo/de boemia etc...", you can picture the guys saying that, or saying that and high-fiving, congratuling each others.
In that way "okay, damn it, the party must go on" of them. That, is if the landlord evicts you next day, so be it!
let´s have that beer and sing and party... A thing to think when one is already tipsy. Enough! high five (my) to my gang/group and our life style
It could be a figure of speech as well, if so, "high five for lowlives'' he would be thinking "it´s okay to be a lowlife, whether you approve of it or not."