- People with Ph.D.'s are not addressed as "Dr". That title is generally only used for medical doctors and, sometimes, if they insist loudly, D.Div.'s, but they really shouldn't be indulged, since the only point of getting that degree is to be called "Dr" when your tradition doesn't let you be called "the Rev. Fr".
- Never inquire about or discuss somebody else's diet/fast [EDIT: or your own, especially your own]. The first rule of fasting club is not to talk about fasting club. And it simply isn't polite to ask if somebody is reducing.
- Quite fortunately, you're not really obligated to get anybody a Christmas gift. But don't go cold turkey: gradually alienate your friends and family first.
- Don't take off your jacket when, for example, wearing evening attire unless you absolutely must [say, if you have to assist a woman giving birth, though if you're qualified to do that, you should've gotten a jacket with cuffs that actually unbutton: it's what they were originally there for]. You're supposed to keep it on.
- Don't throw up on the train. Try to at least make it to the next stop and jump out to the platform.
EDIT: Added "Contraception and Chastity" to the links and created a facebook group about the immorality of contraception.
EDIT: Revised the first point.