Most Helpful Guy
Buy medium, if he's skinny medium probably fits. If he's like uber skinny small will fit him. But when buying online, the sizes usually come in Asian size(Asians are small) So take the medium.
My size is large on everything. I'm not fat, or in any ways "Large", and I'm not skinny either. But medium is just too small for me, so if he's just normally skinny, medium would be the thing.