No, not Perl idioms... but I learnt them in clpmisc:
The answer was:
Well, i can explain its meaning, but I don't know its origin for sure.
From what I can find, it's from the 1920s. A "cool cat" was someone who kept up with all the latest fads and trends. The "cat's meow" was something too cool for words.
Today, Dave Weaver added:
Similar phrases, in terms of both meaning and structure, are "bee's knees", and (mainly UK English, more common, but more coarse) "dog's bollocks".
(emphasis is mine.)
PS: it was my birthday two days ago, would this count as a present?