A personal favourite is, "it's always in the last place you look." Which I've started using, but only in the ironic sense with an internal aside of, "unless you're REALLY stupid and keep looking after you found it."
I find platitudes particularly annoying. To me, it substitutes a basically automatic response for anything resembling thought or meaning. This is most likely an unfair attribution to most other people, so I tend to keep it to myself (the notable exception being when someone tries to cheer me up with some meaningless comment ... on that, I bite.).
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