Absolutely no doubt that fickle minded student will face plenty of obstacles because this student thought of exercising those attributes of non verbal language which are not appreciated at PI.
Speaking with accent, flashing branded accessories, unnecessary framing sentences, avoiding straight answers, claiming high, untenable ideas, wearing party wears with gelled hairs really put off selection panel.
List can be enlarged of negatives but without any worthwhile point of establishing truth that Personal Interview process is judgmental on that given moments so anything which differentiates you with others will be noticed. So remain in the area of positivity.
Humility with positive approach will win you hearts at PI. After all selection panel is judging you on your sagacity, maturity. Simple way for not failing at PI is to ensure that you remain as you are. Be natural as that will automatically create a differentiator between you & others and you will be successful at personal Interview.