To irritate or exasperate. A noun can be used between "brass" and "off" or after "off." Let's leave John alone for now—I think we brassed him off a bit with our criticism.
Irritated, disgruntled, or exasperated. Primarily heard in UK. John's just a bit brassed off with us at the moment, so let's leave him alone.
brass someone off
Sl. to make someone angry. (Primarily military. As angry as the "brass," or officers, might get about something.) You really brass me off. The private brassed off the sergeant.
mod. angry; disgusted. You look so brassed off at the world. Smile!