Secret Service agents yesterday interviewed a “Hill-Man Morning Show” co-host at the WAAF-FM studios in Brighton after he made a threatening comment about President Obama while talking about the national health care proposal. Anthony Parziale, who is known to listeners as “Spaz” on the Greg Hill-hosted morning-drive program, plans to write a letter to Obama to apologize for his remarks and invite the commander-in-chief for a beer, said George Regan, a spokesman for Entercom Communications Corp., which owns WAAF.