“The day of the Lord” does not always mean something pleasant, as Joel revealed,

“Alas for the day! For the day of the Lord is at hand; it shall come as destruction from the Almighty. Is not the food cut off before our eyes, joy and gladness from the house of our God? The seed shrivels under the clods, storehouses are in shambles; barns are broken down, for the grain has withered. How the animals groan! The herds of cattle are restless, because they have no pasture; even the flocks of sheep suffer punishment” (Joel 1:15–18).

Also, as that passage shows, the day of the Lord does not have to refer to the Second Coming of Christ, but the day of the Lord simply means a time when He visits with judgment, which often means condemnation.