Step 1: The key word is except, so identify the three true habits first and the leftover is the answer.
Step 2: Habit disorders cluster around tic disorders and body-focused repetitive behaviours - so tics, nail biting and thumb sucking all belong to this family of involuntary, tension-relieving acts.
Step 3: A temper tantrum is different in kind - it is a goal-directed emotional explosion driven by frustration, fully experienced by the child, and not a quiet automatic repetition.
Step 4: The behaviour that is NOT a habit disorder is the tantrum.
\[\boxed{\text{Temper tantrum}}\]