To have a cup of coffee technically means a brief trial in the Major Leagues by a player or a pitcher. A rookie, often called up in September, will get their first taste of the major leagues and it will often be short. Figuratively speaking it's barely long enough for them to drink a cup of coffee.
Baseball Almanac has posted below a list of every former Major League player who had exactly one cup of coffee, or in terms of baseball statistics, played exactly one baseball game. Some pitched exactly one game (and never had an at bat), some batted in a game (and never fielded), some pinch ran (and never batted or fielded), but they all have had exactly one cup of coffee.
NOTE: The Cups of Coffee script is sortable! Click any column name (Only Game, At-Bats, Triples, Home Runs, Earned Run Average, Strikeouts) to see which cup of coffee player is the leader in that particular stat.
"Why did Paciorek drift into baseball obscurity-and immortality-after that brilliant debut? Interviewed in San Gabriel, where he now lives, Paciorek said a chronic back condition deteriorated after the 1963 season. Though he was invited to spring training the next season, severe pain limited Paciorek's success and forced him to undergo back surgery. He never again reached the major leagues. Even so, no one can take away The Game. 'It was like a dream-I couldn't believe it was happening,' said Paciorek , who is billed as a 'one-day wonder' in the 1990 Guinness Book of World Records. 'I don't know why, but everything seemed to slow down when I faced major league pitching.'" - Sportswriter Steven K. Wagner in The Los Angeles Times (01/31/1991, 'It's All in Day's Work : Baseball: John Paciorek was three for three in his 1963 debut for the Colt .45s, but he never played in another major league game', Source )
Baseball Players Who Appeared in Exactly One Major League Game