This is a word that you use when it has been a long time sincu you have hade yourself a girl. Fett=Pussy, and Laus=to be without. So when your "fettlaus" you dont got any pussy to attend to.
I have been "fettlaus" a long time now. My girl just broke up with me so now I'm fettlaus.
ayon kay Darkwatch ika-27 ng Enero, 2006