Tell him he needs to get to the doctor before it gets infected and kills him. It is no laughing matter, and he's not being a wimp. My brother-in-law was hospitalized more than once for poison ivy, and had to have massive antibiotics as well as antihistamines.

Wash or even discard whatever clothes he was wearing when he got it, and anything they came in contact with. The oil can linger, and cause a reaction again.