a. A hangover, or a symptom of one.
b. transf. and fig. An unpleasant aftermath or reaction; depression, ‘blues’; clamour, uproar.
c. Katzenjammer Kids (or Children), mischievous, naughty children; enfants terribles. So called from the title of a comic strip, first drawn by Rudolph Dirks in 1897 for the New York Journal, featuring Hans and Fritz, two incorrigible children. Also attrib.
**Watch our for us Katzes. We come with aftermath.
(definition culled from the wide & glorious Oxford English Dictionary)