I think you encounter bad words like F word less than in movies, but maybe some populations like teenagers or college kids will use it more. Friends might use it also but I never use those bad words and I only have 1 friend who uses bad words on a regular basis. I guess it also depends what kind of friends you have. I don't think those words are necessary and frown upon them, especially don't use them at work. I am not sure about formal speech - what formal speech are you thinking of?