This topic seems to come up quite a bit.Most if not all people have no clue when it comes to etiquette.This is what i do,i give them a minute or two to ask if they can join.If they don;t ask and continue to BS about other stuff i ask them what there intentions are.I let them no that i don't mind if you join in just give me some room.Or better yet i ask them,you're not thinking of fishing here without asking are you,cause that would be rude.More often then not they walk away or we have a good time fishing.