when a couple sitting at a restaurant is approached by friends it is customary that the male will stand to greet the visitors - it is not mandatory for the female to stand, and depending on the age of the woman, visitors might wait until the lady extends greetings towards the approaching individuals, before they formally greet her.

in very formal situations males are expected to rise whenever a lady leaves the table, and do the same when she returns - for large groups, only the people sitting to the left and to the right of the lady rise, instead of the whole group.

also applying to large gatherings such as birthday celebrations, very popular in rio's restaurants, visitors should know that if or when someone at the table commits a gaffe, or says something inappropriate, it should be ignored - trying to backtrack or fix a gaffe makes the situation worse, best to change the subject and move on.