1. A day in which someone experiences misfortune, difficulties, or negative events
Yesterday was a bad day for you, wasn't it?
Ontem foi um dia ruim para você, não foi?
2. A period of 24 hours during which things go wrong or do not proceed as planned
It looks like it's been a bad day for you with all these problems.
Parece que foi um dia ruim para você com todos esses problemas.