1. Ruined, spoiled, or made worse; messed up.
Usage: British informal; often used in the phrase 'naffed up'

Examples

• I naffed up the presentation by forgetting my notes.
• The whole plan got naffed when the weather turned bad.
• He naffed the repair job and made it worse.
• Don't naff it up this time—we need this to work.
• The system was naffed after the update.