@Offbeat @noobster he is actually friendly, always smiling - I think he simply has no personal care and has no idea others find him repulsive. But because he is otherwise not being rude I just don't feel comfortable handing him a towel and asking him to clean himself or openly skipping him, both options are quite close to directly telling him "sorry you disgust me please take a shower." I will tell the instructor and see what he will do with it.
@Offbeat btw I'm really curious if you had to take some guys aside to tell them that girls complained, how did they take it? I have to say if someone told me that people are complaining about my smell/sweatiness, I would be so embarrassed I would probably never ever come back (I guess a win for others if someone is smelling that bad that others have to tell him/her). In the past, I had a teacher who during every class kept saying (to no one in particular) that it is not acceptable to show up with bad hygiene, I wish more teachers did this.