1. lacking order, system, or planning; not properly arranged or structured
Usage: British English spelling; American English uses 'disorganized'
2. (of a person) unable or unwilling to plan and manage tasks effectively
Usage: British English spelling; American English uses 'disorganized'

Examples

• The files on her desk were completely disorganised.
• He is a disorganised person who often forgets appointments.
• The event was poorly planned and rather disorganised.
• Their disorganised approach to the project led to delays.
• The kitchen was disorganised after the party.
• Without a clear system, the office became increasingly disorganised.