Just to clarify, vinegar dissolves calcium deposits from hard water -- in other words, it's for cleaning hard water stains, like on your windshield.
When your headlamp lenses are cloudy, it's not from hard water, it's from being pitted by dirt and road grit. They need to be polished, preferably by machine. As SpecC pointed out, you could sand first with a fine grit and then polish by hand, too. But no matter how you tackle them, it won't be with "household items." You'll need to buy a few things.
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