Seems Ben Affleck knocked back a few at a Halloween party in Los Angeles after staying sober for more than a year, Us Weekly reports. The Triple Frontier star—or what looks like him, behind a skull mask—was caught by TMZ leaving a Unicef ball in West Hollywood on Saturday night, his gait noticeably unsteady. But 47-year-old Affleck, who's gone to rehab before, has already said he's likely to fall off the wagon now and again. "Sobriety is difficult and elusive for everyone struggling with addiction," a source tells the New York Post. "Ben has acknowledged he's going to slip up from time to time … it was never as if this was simply behind him." (More Hollywood stories.)