It was inspired by same theme as Blank Generation by Richard Hell (whose punk lyrics and fashion, ripped t-shirts and safety pins, inspired Sex Pistols manager Malcolm McLaren when he visited NY in 1975). Pretty means "mostly" and "vacant" means offering blank stares, poor or no verbal responses, just useless. The song is of course sarcastic. We're always out to lunch, meaning clueless, useless. Of course we really know how we feel (angry, bored, alienated) but when you treat us like machines or children, we can certainly pretend we're stupid, but we know it's a put-on. You adults might be upset with our passivity, but we don't even care, we'll go on being alienated, we'll keep on scowling and upsetting you with our vacancy. We'll live life our way, so buzz off and leave us alone. Not just Blank Generation, but one could argue that an even earlier song of this type is the Who's My Generation.