It COULD very well be that the company you have invited over may have scents of their own pets on them and it's aggravating him. That's what happened when I started pet sitting at my cousin's house. His cat LOVED me when I first went over there. Now that he's on vacation, she's growling and hissing at me. Go figure.

Like others have said, it could also be pain from arthritis in their declawed paws.