I have had to in the past. A chap in one of my groups was coming with clothes that were apparently never being washed and neither did I think he. I found myself put in the position by others to be the one to have the chat. I, politely as I could, asked him if he had access to laundry and cleaning facilities. He did, and he was aware he smelled. It turned out in his case he had the delusion that the smell would ward off evil. it was a difficult conversation as I had to advise him he would not be welcome unless he looked after his self care. He eventually did.

More recently I was on a shuttle bus that was squished standingroom full. Someone was so bad the driver had to stop and ask him to get off. Now that must have been humiliating.