Indicates strong agreement to a comment made by someone else, especially when that persons comment is a bit of an understatement, or states the glaringly obvious, or both.
Effectively equivalent to the phrase "That ain't no lie!!" or "Ain't that the truth?!", but said with great enthusiasm.
During a heavy thunderstorm, your friend says "It's a little bit wet outside." You respond with "You ain't shittin' kittens!!"
Two retail employees get done dealing with a difficult customer. In private, one says to the other "That guy was a douche!" The second responds with "Pfff, you ain't shittin' kittens!!"
Being exceptionally excited about something. Saying, "I'm excited about this," only says so much and can be taken in so many ways, but if you say, "this has me shitting kittens," there is no contesting the level of awesomeness that must be awaited.
Scammon: You excited to see Mr. Bungle tonight?
Noah: You kidding me? I'm shitting kittens!
a woman whose vagina during arousal begins to ejaculatefluid in a stream or gushing fashion.
Before I begin any sexual act with my wife, I have to lay down a towel, for she has a spittin' kitten, if I don't I have to wash the bedding everynight.