I am sorry but I do not understand your sentiment here - If I am sitting in First or Business Class, and have either paid for the ticket myself (or my employer has). I should be able to wear whatever I want.

A 16 hour journey is not the time and place for a suit, and given the high chances of food/drink spillage over that time (either my own fault or someone else's), neither is anything smart. Baggy combat pants, loose shoes, old polo or t shirt do the job fine for me. I do make sure there are no holes in my socks now though.