Every now and again, Marvel Comics would release a special edition comic book with double the number of pages and dub it “Giant-Size”. Comic book fans will remember Giant-Size X-Men #1, which introduced many of the X-Men from the movies and revitalized the series, which was in a slump at the time. There were a number of Giant-Size Spider-Man team-ups, and Giant-Size Avengers.
Marvel Comics has a character called Man-Thing, and when they giave him a book with double the number of pages, they got an unintentionally phallic title…
Thanks to the anonymous commenter for the tip!