Macaulay Culkin. When’s the last time you heard that name? Many were surprised by yesterday’s reporting that the “Home Alone” star has joined the Season 2 cast of “Fallout,” which claims he’ll be playing a crazy genius. Culkin has acted in only four movies these last 20 years, all of them very low budget affairs (“Sex and Breakfast,” “The Wrong Ferrari,” “Adam Green’s Aladdin,” and “Changeland”). The “Fallout” gig will be his starriest role since 1994’s “Richie Rich.”