Something is disconcerting if it makes you uneasy or unsettles you. Even if you don't give your little brother's dreams of conquering the world and enslaving humanity much chance of success, you may find them disconcerting.
Think of a concert as something that is organized and runs smoothly. Anything that interrupts that organization and causes concern is disconcerting. The fact that your band ends each rehearsal with a screaming match is disconcerting, unless they are a punk band. Your disconcerting habit of laughing hysterically during job interviews? That may prevent you from gaining employment.