Santiago Segura and Florentino Fernández star in this gross comedy that tries to follow the path of teenage comedies like "American Pie" or "Dude, where's my car?", in which a great deal of the gags are based on bodily fluids. The result is funny only intermittently, and I had the impression that I had already seen most of the gags somewhere else.
The two leading men seem to have been born to play these characters, although that is not to say a lot. I found Florentino Fernández much more convincing than Segura, but again, that doesn't mean a lot. Newcomer Jaydy Mitchell should stick to modeling or whatever she does as a day job, since hers is one of the worst debuts I have ever seen. The supporting players (Miriam Díaz Aroca, Elia Galera, José Luis Coll) deserved better roles and a better film.
In any case, "Isi/Disi" is acceptably entertaining but it offers nothing new. If you like gross gags and smutty jokes, then this is your kind of film. If not, better go and watch something else.