know something inside out
know something like the back of one's hand
know something or someone for what it/he/she is
“Know something like the back of one's hand.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/know%20something%20like%20the%20back%20of%20one%27s%20hand. Accessed 7 Dec. 2022.
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