Not an other adult.
I've told my kids, when they were adolescents, "Hon, you really need a shower. OK?" Young adolescents sometimes don't realize they need very frequent showers.
But, other adults, no, I never say anything. Maybe once in a while, after my husband has been working in the yard and he's already joking about how much he smells (which isn't much. The Man has an incredible resistance to B.O.) I'll tease him about it. But, not someone who really smelled.
Do adults who don't shower regularly don't realize? Or do they have a faulty sense of smell? I don't know.