Well, it's a joke name, sir.
2 seconds sound clip from the Life of Brian movie soundboard.
You can hear this line at 00:40:22.602 in the Blu-ray version of the movie.
Quote context
[...]
- Centurion, do you have anyone of that name in the garrison?
- Well, you sound very sure. Have you checked?
- Well, no, sir. I think it's a joke, sir. Like, uh, Sillius Soddus or Biggus Dickus, sir.
- What's funny about Biggus Dickus?
- Well, it's a joke name, sir.
- I have a very great friend in Rome called Biggus Dickus.
- Silence! What is all this insolence?
- You will find yourself in gladiator school vewy quickly with wotten behavior like that.
- Wait till Biggus Dickus hears of this.
[...]