Anecdotal sources suggest that the idiom used by Doc Holliday in the movie Tombstone “You’re a daisy if you do” means you're the best or the most marvelous.
In the late 19th century "daisy" was a common slang term for "the best in its class. It was a fairly fashionable term in the late 1870s.
If you look through old newspapers from the time period, there are plenty of references to people being daisies because they were doing something wonderful for their town.
In latest news, Val Kilmer (Doc Holliday in the movie Tombstone) is ringing in 2015 lighter, healthier and eager to begin work on what he's deemed his "dream role." Read more at MNN.com.