Untagging is definitely not rude and is certainly preferable to, say, hypothetically...
Showing the photos to your boyfriend (who is NOT my FB friend and otherwise would not have seen the photos that were posted), and complaining about how awful they are and what an embarrassment they are, such that he gets irate on your behalf and, the next time I have to see him, makes tons of passive-aggressive remarks about how rude it is to post photos on FB without the subject's permission. Meanwhile, the subject of the photos has not said a single word, and, additionally, left herself tagged in the photos. (If it makes a difference, the subject was my niece and the photos were from her childhood.)
So, yes, I think the way to handle unflattering Facebook photos is to untag yourself, and, if you really don't want other people to see them, very politely request that the poster remove the photos from their album.