The phrase Mohammedan is offensive to virtually all muslims in much the way that "Nigger!" is offensive to people of dark skin living around the world. A Mohammedan is someone who worships Mohammed. A muslim is someone who worships Allah, and practices the religion of Islam. This isn't a small point, getting it right is likely to prevent many punches in the face when visiting abroad.... So consider this a public service announcement! :-)