Tom wearing an "American Classic"
The Big Daddy-O Surf Special was a classic American luau shirt, introduced on Earth ca. 1962.
Tom Paris was showing off his replicated surf special to B'Elanna Torres before attending an authentic Polynesian luau hosted by Neelix in 2373. (VOY: "Alter Ego")
In the Star Trek Encyclopedia, 4th ed., vol. 1, p. 83, the term "big daddy-o" was described as a slang expression for the subculture of beach and surf popular in Hawaii and California.