(I often refer to S as my best friend in, say, work conversations, despite the juvenile feel of the phrase. It's a bit reductive, in the way you have described, but quicker and more polite than "this person is allowed to touch me, stand behind me, witness my medical frailties, and offer me physical assistance in ways that will get other people bit.")
Don't forget "act as bodyguard, terminally confuse relatives for fun and profit."
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Don't forget "act as bodyguard, terminally confuse relatives for fun and profit."