I frequently hear the f-word and other profanity used in casual conversations at shul, the Shabbos table, and the most holy of Jewish occasions.
I think Reform and Conservative Jews may be less likely to use profanity in shul than Orthodox Jews because while the typical Orthodox man will frequently go to shul every day, the typical Reform Jew will go to temple about three times a year. When you go to synagogue rarely, the solemnity of the occasion may affect your speech.
I grew up a Seventh-Day Adventist Christian and I can’t get used to profanity in casual speech, particularly in a shul.
For Protestants, the use of profanity indicates that you’re not truly born again. That you haven’t truly accepted Jesus into your heart. Protestants tend to be nice people. They don’t tend to say uncouth things.
From a Jewish perspective, they frequently seem fake. When a Jew clicks around the website of a Christian college like Loma Linda University, the niceness seems unreal. Compare it to the website of Yeshiva University.