Get him some of that crystal stick deodorant, it actually works until your armpit bacteria adjust to it. Usually you’ll get a year or so use out of it before selection grows exclusively resistant bacteria.
I had a housemate who was into Facebook health influencers at one point, absolutely nothing would reach him when we told him “you stink, you need to keep yourself clean.” We had to punt him, the BO was just one of the problems we had with him.
This 👆 - you stop noticing that you smell when you smell all the time. Setting up tests is just avoiding the real solution which is an uncomfortably honest conversation.