Well, the Ides of March is just one day, not the whole month.
September is only cruel if she gives you bad news when she comes back from summer vacation. SEE YOU IN SEPTEMBER - THE HAPPENINGS
Not sure what's so bad about December. I guess Aqualung didn't like it's "foggy freeze," and that it's a pretty dry time for watching "pretty panties run." Jethro Tull - Aqualung
Gordon Lightfoot didn't have too much positive to say about November: "The Wreck of the Edmund Fitzgerald" - Gordon Lightfoot.
One cruel day in a month tends to label the entire month cruel.
September - 9-11
December - Pearl Harbor