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Coleman was born in Orlando, Florida on August 25, 1937. He signed as an undrafted free agent with the Washington Senators at age 18. He was released by the Senators and signed by the Los Angeles Dodgers, then taken by the Philadelphia Phillies in the rule V draft. In 1961 he appeared in 34 games for the Phillies, getting hit by a pitch in his first Major League at bat. He would hit only .128 for the Phillies that year in 47 at bats. The Phillies finished in last place that year, a spot soon to be taken over by the expansion New York Mets franchise. In the off-season, the Mets selected Coleman in the expansion draft. He would play parts of three seasons for the Mets, hitting .205 in 415 at bats.
While Coleman never had great success as a player, he became somewhat famous for his malapropisms. Perhaps most famous was an interview on Kiner's Korner, the Mets post-game show. Host Ralph Kiner asked Choo Choo "What's your wife's name and what's she like?" Choo Choo replied "My wife's name is Mrs. Coleman and she likes me, bub."  Another time Kiner asked Clarence how he had gotten the name Choo Choo. "I don't know, Ralph." was the answer.
Upon first introducing Choo-Choo to the media, Mets manager Casey Stengel didn't exactly sing his praises. He said of Coleman "You have to have a catcher or you'll have all passed balls."  But he did refer to him as "the best low-ball catcher in baseball", a commodity the early Mets staff probably needed.
In 1963, during Duke Snider's only year with the Mets, he told a reporter how Choo Choo didn't know his name. Having spent months on the same team, the reporter didn't believe him. To prove his point, Duke said to the Met catcher, "Choo Choo, do you know me?" Choo Choo replied, "Yes, you're number 4." Roger Craig once said: "Choo Choo would give you the sign and then look down to see what it was." 
The authors of The Great American Baseball Card Flipping, Trading and Bubble Gum Book, Brendan C. Boyd & Fred C. Harris, Little Brown & Co, 1973, had this to say about Coleman on p. 37, next to a picture of his baseball card: "Choo Choo Coleman was the quintessence of the early New York Mets. He was a 5'8", 160-pound catcher who never hit over .250 in the majors, had 9 career home runs, 30 career RBIs, and couldn't handle pitchers. Plus his name was Choo Choo. What more could you ask for?"
- Career statistics and player information from Baseball-Reference