I was surprised when my colleague told a waitress to pick the proper thing for him when ordering in an Izakaya restaurant.
Everything is suitable and right. Therefore it is appropriate and proper. Strangely enough, this also means irresponsible. Maybe it's because when everything is suitable and right for you, you're taking too much and not leaving enough for everyone else, making you irresponsible?
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.