Approach this by asking when a psychiatric assessment can actually give a valid result. A reliable suicide risk assessment depends on a clear sensorium. In someone who is acutely and severely intoxicated, judgment, speech and emotional state are all clouded by the substance, so any conclusion drawn at that moment is unreliable. The correct emergency action is to treat the intoxication, monitor safety, and assess later once the patient is sober. Hence intoxication does not call for an immediate specialist review; it calls for medical stabilisation first.
Contrast this with the other choices. Formal thought disorder signals active psychosis, a state strongly linked with impulsive and unpredictable suicidal behaviour, so it needs urgent psychiatric input. A chronic severe physical illness is a well documented driver of hopelessness and completed suicide, especially in older patients, and must be evaluated quickly. Social isolation removes protective support and is itself a strong predictor of suicide, again warranting prompt attention. All three sharpen the urgency, while intoxication delays the meaningful assessment.
So the single feature that does not mandate immediate specialist assessment is acute severe intoxication.
\[\boxed{\text{Acute severe intoxication}}\]