stultify

(verb) prove to be of unsound mind or demonstrate someone's incompetence. Example: "Nobody is legally allowed to stultify himself."

(verb) cause to appear foolish. Example: "He stultified himself by contradicting himself and being inconsistent."

(verb) deprive of strength or efficiency; make useless or worthless. Synonyms: cripple. Examples: "This measure crippled our efforts." "Their behavior stultified the boss's hard work."