That crevice is not his arm pit though...it's just a sweaty roll.
I don't understand how any adult can allow themselves to get anywhere near that point.
I know with my infant daughter who has some healthy baby rolls...you gotta keep those crevices clean or they get all sticky and nasty and can get sore...keeping up with that as an adult...gross.
Unfortunately for the rest of us, they don't all keep up with their cleaning.