The expression HIT IT OFF means to become friends, to get along well.
Here are some examples:
When I first met her, I knew we’d hit it off with each other immediately. And so we did.
We’ve lived here next to each other for years, but still, we’ve never really hit it off.
Anne, this is John. You have so much in common. I’m sure you’ll hit it off.
I thought you two would hit it off, but now I know that just working together is not enough.
We both tried, but it looks like we didn’t hit it off after all.
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