Normally the reason you don't get a knife when you ask for one is because the person you asked is emo.
Emo Knife Reluctance
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Explanation
Experiment
Explain Bear
Listen up, buttercup. The joke plays on a dumb stereotype that emos are always sad and want to cut themselves. That's why they are reluctant to give knives to other people because they might use them for self-harm, which is a pretty dimwitted thing to joke about, especially for someone as clueless as you.