A person that is excessively moral or modest, not only in sexual matters, but also in matters concerning mischief, alcohol, drug use, and other things. The word is often used in teasing, mocking, or insult.
John: Aw man, I can't believe Sheila's going out with Brad. I love her!
Pierce: Hey! I have an idea: *takes out a package of powder* Let's put this fart powder in his drink. What a date it will be!
John: What?! We can't do that, it's wrong! Besides, if she's happy with him, then I'm satisfied.
Pierce: Geez, John, you're such a prude! You really oughta be a little more, well, competetive, if you wanna get a girlfriend.