Hollywood loves looking in the mirror, even when it’s embarrassed by what’s staring back (which, frankly, isn’t often enough). What Just Happened, Barry Levinson’s riff on producer Art Linson’s 2002 movie-biz memoir, has more clichés than a season of Entourage: weaselly agents, spoiled stars, and sleazy foreign financiers with statutory arm candy. De Niro, taking a break from broad comedy (thank God!), shines as a frazzled producer with two exes and a pair of celluloid nightmares — a pretentious Sean Penn flick whose ”edgy” ending features a dog getting shot, and a big-budget headache starring Bruce Willis, who refuses to shave his bushy, Talmudic beard. The message is: Everyone in Hollywood lies…mostly to themselves. The point is proven all too well on the EXTRAS commentary when Levinson and Linson crack up at their own wheezy gags. B?