Have you ever done any public speaking? I am an accomplished public speaker (I actually enjoy it). But, under the pressures of the moment, have experienced far worse mental lapses than replacing "heck" with "hell".
Once, speaking to an audience of about ninety (a small audience for me) on a subject on which I am a recognized expert, I twice referred to a friend as "Williams", instead of the correct, "Richardson". Something felt vaguely wrong, but, it wasn't until he pointed it out afterward, I realized what I had actually said...
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The girl is only a high school senior -- speaking to (probably) the largest audience she had ever faced -- at a high point in her life. Drop your holier-than-thou attitude -- and give the young lady a break!!