What if it was intentional? Or at least, it was exaggerated on purpose to make the point? Would you have considered it contemptible if the guy has just blurted out, "This is BORING."?
Indeed, yawning is a natural reflex of the body over which humans have very little control.... Hence, to fine a person for yawning in court would be like trying to fine someone for hiccuping, or for having an asthma attack, or for having a parkinsonian tremor.
Horse manure. You have PLENTY of control over how your yawn progresses. Can you stop it? Not necessarily. But can you keep it relatively quiet? Of course. Can you cover your mouth with your hand? Absolutely. Can you make it loud on purpose? Absolutely. Can you open your mouth even wider and sway your head to exaggerate the motion? You bet.
I mean, please, if you haven't faked or exaggerated a yawn to make a point then you haven't lived :)