He leaves the room for a reason (ie to get a drink from the fridge). During which time he may breifly touch his straight males buttocks in a jokeing manner.
He goes to another room and calls his desired male into the room and talks and drinks a little then gets hard while his friend is there, subtly indicating it. If his friend seems uncomfortable he retorts his actions as "am only joking".
Though if his straight friend shows a subtle intrest through body language or more obvious hint, the "shnooby"becomes more intentful and senuale with his "prey", which ends in either felacio or penatrive sex.