Blumpz, I am betting that it is the arm that he also holds his phone to his ear/head/face with and that he holds it in a position that makes that pit sweat. Tell him a story about some badass headset you got or something. No more holding long convos to his face causing him to sweat. It will help with neck and shoulder pain too making him more pleasant(assuming a guy that sweats profusely in one pit is unpleasant).