I have no faith in myself to speak coherently about this silly farce. But I do have faith in Jesse Einserbeg. Yes, I liked “Zombieland” and “The Social Network” that much and I’m eager for his next, “Batman Vs Superman” with Ben Affleck and Henry Cavill. Ok so here are the facts: Einsenberg goes crazy in “American Ultra” as a stoner who may or may not be a government agent. Kirsten Stewart plays his girlfriend and they’re both targeted for extermination. Or something like that. The movie is just an excuse for laughs that come fast and raunchy. Unfortunately, the laughs run out of gas only halfway through. What was meant as an entertaining stoner flick quickly turns into one giant action scene that refuses to end. Damn shame. Eisenberg and Stewart, who previously worked together on the underrated “Adventureland”, have chemistry. Too bad the movie isn’t half as good as they are.