Lisped variation of the phrase "Kitty Kisses", or to kiss a kitten.
Originally, a gag where the aggressor puts his finger into the mouth of a feline and then into the mouth of his unsuspecting victim, yelling out in a fruity fashion, "KITTY KITHES!!!". Often accompanied by an open fingered, vigorous clap to show unbridled excitement over the smiting of ones enemies in such a ridiculous fashion.
More recently the term has been used to show any kind of excitement (sexual or otherwise) to a gathered group of friends.
Also used to make strangers uncomfortable in public. Occasionally used in the same manner "Cheese!" is used in posing for a photograph.
Other known variations include pug kithes and kennel kithes. Both variations use the same fruity tone and fruity hand clapping.
Generally, the fruitier and louder the Kitty Kith, the better. This will result in greater volumes of laughter from your friends.
See also: Sebo, Seabass, Seebs.
Photographer: Alright, everyone say 'Cheese!'.
Group: 'KITTY KITHES!!!'
Photographer: (under his breath) What a bunch of homos...