If you are new to a group of brunchers, there is already a carefully constructed seating situation that you are not welcome to interrupt. Not only is the group arranged by who likes to talk to whom, but there are other considerations.  Factors like who likes to share food, who goes to the bathroom or takes phone calls the most, and who has had sex with the same guys in the past are taken into account. Don't disrupt the carefully calibrated social order. Wait until everyone else has sat down and then take your seat.