The paper concentrates on the description of common proceedings of youth slang in Czech and French. These common word-formatting categories should be characterized as “slang parasystems”. The youth slang of Czech and French teenagers operates with the actualization of the idioms of old slangs, with semantic neologisms and metaphors. Metaphors are frequently “chained” by synonymic and paronymic attractions. The expressive component in neologisms is erased by high frequency of usage, whereby vulgarisms become quickly banalized. The intensity of expressive idioms is very difficult to translate into Czech and French, as we show in the examples.