There were few bad words in my house growing up, and those that were didn't tend to follow the basic four-letter word rule. We weren't allowed to say “I hate you” (although to be fair, hate is a four letter word). “It's too hard” was also frowned upon. But the phrase my mom hated the most was “Shut up.” Saying this would land us in our rooms with no privileges for the bulk of a day.
I didn't even hear the phrase “shut up” until I was in school. I remember by first grade teacher used it often, and it colored the way I thought about her. It seemed so rude and so disrespectful to six-year-old me. As I got older, it became more common for me to hear it from both kids and adults.
I once asked my mom why I couldn't say it. Her answer? “Shut up tells me that what I have to say is not important nor worth hearing. Quiet please tells me that you need quiet right now, but that my ideas and thoughts are still important and perhaps we can discuss them later.” Now as a mom myself, I tend to agree. “Shut up” is confrontational and mean sounding, while “quiet please” is not.
My husband comes from a house where “shut up” was the norm. I found it really off-putting at first and I told him why. Sadly enough, his home was one where children's thoughts and ideas weren't appreciated, and kids were expected to always be silent. He quickly got on board with the no “shut up” rule when we had kids.
Old habits are hard to break, though. Many times he would catch himself saying “shut up” to our young son. Fortunately he almost always caught himself but only after half the word was out. His answer was to turn it into “shush please.” Until one day he failed and instead said, “Shud-ush please!”
My son loved it. He giggled while also providing the necessary quiet, and the next time he wanted quiet he exclaimed “Shud-ush daddy!” So now we are not a shut-up house nor are we a quiet please house. We are a shud-ush please house, and proud of it. I'm not sure if shud-ush is any better than shut-up, but in the end my family sees it as a wonderful inside joke and it doesn't evoke any hard or hurt feelings when it's used.