Why can't I tighten my olive oil bottle?
Oil bottles tend to be opened and closed many times, and the caps deform. They're often made of very thin metal and every time you do them up the metal spreads a little until the screw threads don't engage properly. The oil itself doesn't help as it lubricates the thread so the normal cue that the cap is tight enough -- at least partly due to increased friction -- isn't as noticeable as on other bottles

Plastic caps seem better than metal but it's still easy to over tighten them.

You need to be more gentle, especially when they're new. The better oils I buy have a plastic stopper inside the metal cap that seals without much force. The cheaper ones have the same structure moulded into the plastic cap, so the seal isn't on the thread.