Which is exactly what I did coming out of undergrad University here in the US. I started work and then for fun I went and formally studied German at a local college, taught by a native speaker born in Köln. I was educated to use Sie out of respect and only use du with close friends, children, and only when instructed by co-workers and other associates. In my travels I have had many discussions in German and have not once been repremanded, only on occasion told I am fine to use the informal form.