Green’s Dictionary of Slang

1. (UK black) aggressive, pugnacious; thus get milly, to become aggressive.

1997

C. Newland Scholar 90: I admit he’s a milly brer, but I don’t fear ’im man. [Ibid.] 185: Gimme my t’ings man, ’fore I have to get milly on the situation.

2. (S.Afr. gay) mad, ‘dizzy’.

2003

K. Cage Gayle.