not one's day, this is
not (one's) day
A day that has been particularly stressful, difficult, disappointing, or filled with unfortunate events for one; not a good day. I can't believe I got locked out of the apartment. This is just not my day. I'm sorry, sweetie, I know you studied hard for that test. It just wasn't your day.
See also: not
not one's day, this is
Also, just one of those days. Nothing is going right for one today. For example, The car wouldn't start, it rained unexpectedly-this is not my day, or The phone has rung nonstop all morning; it's just one of those days. [c. 1920]