I'm always hunting for these expressive moments. Japanese people (and perhaps all people in modernized countries) tend to show little emotion while getting about their daily business. While on the street people are just going somewhere, but I try to find opportunities to show them breaking this curtain. Often this means drunkenness.
XDDD i really like such pics because of this fact (like you said) that it's hard to find emotions there ^^... but last year i've also taken pics of laughing people... and yeah they were drunken and made party XD maybe some day i will upload them^^