Not the full quid
Definition 1 of 1
Pro Tip 1/3Cultural Sensitivity
Be aware that the phrase can be offensive as it mocks mental acuity. 
Be careful not to say someone's not the full quid in a professional setting.
Pro Tip 2/3Colloquial Use
Best used in informal contexts among friends who understand the phrase. 
Around Australian mates, you might hear 'he's not the full quid' in a jesting tone.
Pro Tip 3/3Avoid In Insult
Don't use it to directly insult someone; it's rude and can hurt feelings. 
Instead of 'He's not the full quid,' use 'He sometimes misses the point.'