(Last cruise, an elderly gentleman and his family, children and all, continued to stare at me during formal night because of the jeans I mentioned above. It's as if they were offended, like their steak could not be digested in the presence of such an atrocity. I simply smiled and continued eating.)
They are staring at you because you are not dressed appropriately for the occasion. I bet if there was a event like your wedding and your best man showed up in jeans, flip flops and coat you might be upset. Its better, in my opinion, not to go to the event if you can't or don't want to dress correctly.