Green’s Dictionary of Slang

1. to lose committment.

1915

Runcorn Examiner 20 Feb. 7/2: Bradshaw and Tranter played well in the early stages of the game, but they ‘browned off’ all too soon, and, during the second half, were hardly ever in the picture.

2. (US) to blunder, to make a mistake.

1956

S. Longstreet Real Jazz Old and New 148: Musically [...] to break time out of tempo is to brown off [W&F].

3. (US campus) to reject a request for a date.

1967–8

Baker et al. CUSS.

4. see browned off adj.