From Longman Dictionary of Contemporary Englishproudest moment/achievement/possessionproudest moment/achievement/possessionthe moment etc that makes you feel most proud His proudest moment was winning the European Cup final. → proud
Examples from the Corpus
proudest moment/achievement/possession• To this day, this remains Morrissey's proudest moment.• To me, it was the funniest, proudest moment I had ever had in baseball.• It's the proudest possession in my house.• I know that her proudest moment was when she won a prize in high school in 1929, for writing. 