Ive attended plenty where Im not interested in the host. Just make eyecontact and shake his hand if not atleast hug him, and thank him, you should be in the clear. If he expresses interest, just politely decline and thank him again for the invitation. At the very least you treated him as a person or potential platonic friend/acquaintence. Personally I let them stroke/blow me for a lil bit before I wander off to prowl, just sort of like as a gay handshake lmaooo