If one is eating Shalosh Seudos in shul with the rabbi, and the rabbi does not get up to wash Mayim Achronim (because he relies on the opinion of Tosafos that it is not necessary, or perhaps he forgot to wash for whatever reason), may one wash himself (if he is careful to wash always, as the Shulchan Aruch, the Gra, and others require), or is it considered haughtiness? What would be a way to wash without offending the feelings of the rabbi? Should one pretend that he needs to go to the bathroom, and then wash (but then he might miss the zimun)?
When someone does according to most poskim in the Shulchan Aruch, we can’t call that being haughty. Instead it is called “ Vayigba libo bdarcei H-ashem” ( being brazen to do Hashem’s will). It is only haughtiness when a person does an act that is permitted and only exceedingly pious people are careful about this. For example if every choson doesn’t daven maariv the night of the wedding and he decides to daven, or to fast on the fast days that are only for the tzaddikim, then it is haughtiness. But not when you are doing like the Shulchan Aruch and most poskim.
Nevertheless it is a smart thing not to make a show of what you are doing and surely not to o anything that might embarrass the Rabbi. Therefore he should to wash his hands quietly, either beforehand or afterwards in a discreet way. You can answer the zimun and then wash maim achronim and then bentch.
Yam Shel Shlomo Baba Kama 7- 28, Encyclopedia Talmudis “Ga’avah”- Yuharah.