Jordan Firstman broke through during the COVID-19 pandemic with a viral series of mock-confessional “Impressions” (his bit as Mother Nature killing off the human race as a “toxic situation” is a keeper). He’s made traditional short films, worked in the writers’ room for HBO’s “Search Party” and sang about Laura Dern at the Spirit Awards. More recently, there’s been a comedy album, a role on #ILoveLA and plenty of misconceptions about who he really is. But it was his vicious, self-excoriating turn in Sebastián Silva’s 2023 dark comedy “Rotting in the Sun” — playing an amplified version of an obnoxious influencer named Jordan Firstman — that triggered something inside him. #ClubKid, a movingly sincere and wise new film that Firstman scripted, directed and toplined, is the result of three years of self-reflection and discipline. Watching the film, you feel the arrival of someone major. Not every comedy debut gets invited to Cannes. Firstman’s was. (He stood with his mother at the ovat...