I'm a big fan of Arizona Gunslinger's Chipotle Habanero sauce. Its nice and hot with great flavor. My Aunt and Unlce live in Mesa AZ where the company is located so they send me a bottle or two every now and then.
If he just wants burning hot, then get some ghost chili extract.
No flavor at all, just plain blazing hot.
18.5" OTS, 22.5" OTG, CB Silver(Rip), Vintage Coleman Bullet, Pit Barrel, UDS