Of course not. Never, ever use a pen name. Don't you know that writers are some of the most outgoing, attention seeking, and sociable people in the history of the world.
The fact that would would even ask offends me. Don't you know that no one on this forum uses a pen name. In fact, I was told to join this forum we must give them our real names. Why else did they ask for my date of birth, bank account number and social security number when I registered? Because they wanted to confirm I was a real writer.
The only reason to even be a writer is to tell everyone you write. Whether it's novels, non-fiction, short stories, deep-emotional-life-shattering poems from high school, that very tasteful gay sex scenes from our favorite fan fiction, or that witty blurb I thought of while watching Jeopardy last night... We must take every opportunity possible to flaunt our writings. Whether it's to nameless, faceless people on the internet or to anyone who was lucky enough to step into an elevator with us (that's what the emergency stop button is for).
So, in conclusion, no pen names. Ever.