It'll be a long day in January
describing something that will never happen
e.g. It'll be a long day in January when you beat me at basketball.
Mad as a March hare
acting crazy (hares act crazy during their March breeding sesons)
e.g. I like John but he acts as mad as March hare.
April showers bring May flowers
rain in April = flowers growing
e.g. You hate this rainy weather but remember April showers bring May flowers.
when one person in a relationship is a lot older than the other
e.g. People ...