The same as worst day ever, but it's in usage when the entire month so far, sucks because of every small mistake you did on the day before.
I got fired two days ago, because I did a prank on April fools day. When i applied to a new job the next day, I didn't get it because I couldn't sleep the day before. Today I got banned on my favorite website for a false claim, of something that happened yesterday. Worst Month Ever so far.