Green’s Dictionary of Slang

(US) someone who is dressed up; thus out on a dike, dressed up specially for a particular event or visit.

1872		Schele De Vere Americanisms 597: Dike, denoting a man in full dress, or merely the dress, is a peculiar American cant term, as yet unexplained. To be out on a dike is said of persons, mainly young men, who are dressed more carefully than usual, in order to pay visits or to attend a party. It is not unlikely that the term is merely a corruption of the obsolete dight, which meant decked out, and is in this sense used by many old English writers.
1892		Newcastle Courant 26 Nov. 2/3: Americanisms [...] A person in full dress is spoken of as a ‘dike’.
1908		L.W. Payne Jr ‘Word-List From East Alabama’ in DN III:iv 305: dike, n. A display of dress. ‘He’s on a big dike to-day.’.
1915		L.R. Dingus ‘A Word-List From Virginia’ in DN IV:iii 182: dike, n. and v. Display in dress.