Green’s Dictionary of Slang

brown off v.

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

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

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

[US]Baker et al. CUSS.

3. see browned off adj.