Ginger is slang for a person with red/orange hair.

hii, i search that and i have maybe an explication. In England, call someone a "ginger" is an insult. So I think this sentence mean the monday is not a good day^^

Red heads are often treated as an outcast in America. Ginger is one word for them. Mondays are looked down on too. Someone is making a silly comparison between things that are both somewhat the "butt of jokes."