Straight to his face.
We actually have a really great relationship. The rest of the office is totally brainwashed about vaccines and other leftist bullshit, so I'm the only one who is openly refusing to get vaccinated. He came to my desk to tell me about how Walgreens is offering vaccines to basically anyone and I said "that's great news for people who want the vaccine." He asked me would I really not get it? "Nope." Why? "Because I don't like it, I don't think it's necessary, it's an experimental injection and not even technically a vaccine, I believe in my immune system and I don't like how it's been socially engineered and forced upon the public. I don't like it."
He was silent.
I continued with "and so if you decide vaccines are mandatory, I'll be working from home." He said, "well, if vaccination was mandatory and you refused, you'd have to find another job." I said, "yep."
"You'd find another job?"
"Yes, I would." I was on my way to deliver something to one of my interns on the other side of the office, so that's where the conversation ended.
I love this but for anyone else reading, the absolute best way to go about this with your boss is to simply say you are open to taking it when (and IF) the FDA officially approves it. This way you sound very reasonable in front of ANYONE. I'm saying this as a medfag (I've had to deny it many times already).
Under emergency use, it is ILLEGAL to make mandatory for anyone. They are relying on virtue signaling and guilt tripping right now to get everyone vaccinated and it wont' work.