A person who demonstrates an exaggerated conformity or propriety, especially in an irritatingly arrogant or smug manner.
Use: I have flung myself in front of your great, socking Bentley so that I can seek medical advice on behalf of my patient because her relations are out to kill her. I dearly hope this doesn't make me sound like a prig.
Americans would say goody-two-shoes. Potty mouths could say tight-[REDACTED]. In Mormon-speak we might call that up-right square a Molly. Any way you slice it, it isn't a compliment.
Which, I admit, presents a problem for those who want to do the right thing. I like how Anne Shirley puts it:
Anne Shirley: Fred is... extremely good. (read: a prig)Isn't that just like our RDDs? Someone who could be wicked and wouldn't...
Marilla Cuthbert: That is exactly what he should be! Would you want
to marry a wicked man?
Anne Shirley: Well, I wouldn't marry anyone who was really wicked,
but I think I'd like it if he could be wicked and wouldn't.
Marilla Cuthbert: You'll have better sense some day, I hope.