Size: Two sentences, and less than 200 characters.
(An explanation might be in order. There was a fanfic contest a few years ago where all stories had to be longer than two sentences and 200 characters. Thus I set out to prove that a story in fact could be just as short and still be a story. The result can be seen below... but I suppose you really have to know the rather special circumstances around that particular kiss for it to make sense.)
Taking your chances.
"You kissed Gabrielle and got away with it!" Joxer exclaimed, his eyes wide with wonder.
"She thought it was Xena" Autolycus answered with a smug smile.