The title is similar to Rocko's catchphrase in which that a day "is a very dangerous day", (e.g., "Garbage Day is a very dangerous day.").
The Church of Jesus Christ of Latter-day Saints | Green Day | One Day International | New Year's Day | Boxing Day | Memorial Day | Seventh-day Adventist Church | Labor Day | Doris Day | Earth Day | May Day | Sandra Day O'Connor | Valentine's Day | Record Store Day | Mother's Day | Ferris Bueller's Day Off | Bastille Day | Six-Day War | April Fools' Day | Australia Day | Father's Day | Brightest Day | Big Day Out | Macy's Thanksgiving Day Parade | Canada Day | Victory in Europe Day | Long Day's Journey into Night | Armistice Day | The Day After Tomorrow | Stockwell Day |