Alec Baldwin got a big laugh after the screening of “Last Day at Shea” at East Hampton’s Guild Hall Saturday night during a Q&A with Billy Joel, the star of the sarcastic look at fame in the 1970s and ’80s. Noting Joel’s ex-wife, Christie Brinkley, in the crowd with Lorraine Bracco, Alan Alda, Rosanna Scotto and Bruce Weber, Baldwin said, “Billy, how do get your ex-wife to attend your movie premiere? As most of you know, my relationship with my ex is a little different than that.” Baldwin’s ex, Kim Basinger, likely wouldn’t spit on him if he were on fire.