I don't think he wanted the beer for beer's sake - I think he wanted it so he'd have an excuse to stay, hoping she wouldn't make him leave... We're shown he has money (although who knows how!) so he could easily afford to pay for the second beer, himself, but she still insists he go.
"Your mother puts license plates in your underwear? How do you sit?!"
Thanks. I couldn't remember if the launderette scene was directly previous, or not... I knew we see him begging, but everybody there walks past - although I suppose he must find success every so often!
"Your mother puts license plates in your underwear? How do you sit?!"