From Longman Dictionary of Contemporary Englishhit it off (with somebody)hit it off (with somebody)informalLIKE somebody OR something if two people hit it off, they like each other as soon as they meet I knew you’d hit it off with Mike. → hit
Examples from the Corpus
hit it off (with somebody)• Ally's jealous that Matt and Ceara hit it off.• Billie had joined Lily and they had obviously hit it off.• Glad you and Edward have hit it off.• I think, in the end, they just didn't hit it off.• They hit it off from the first.• She and I hit it off immediately.• They ended up in the same case study group and hit it off immediately.• If two gardeners hit it off, they can go private through electronic messages in a sort of letter-writing setup.• Knowing both of them, I knew they would hit it off when they got to know one another better. 