1.  Do you have to attend the office Christmas dinner?

Yes, absolutely.

2. Office holiday party etiquette

If there is anything you won't do in front of your boss in the office, don't do it at the party.  It is an office party afterall, be professional,  dress appropriately and stay sober.  Don't do anything that you may regret later. 

3.  Dealing with special dietary issue.

If you are hosting the party, ask your friends and relatives if they have any allergies or other dietary issue. Be considerate enough to accommodate them.

3. Importance of the R.S.V.P.

Don't ignore the request for RSVP.  RSVP is a French phrase "repondez s'il vous plait", meaning "please respond".  The host needs to know how many people are attending so he or she can plan the event.

4. Know when the party is over

If you are invited to a friend's or relative's place, don't overstay your welcome.  Look for cues that the host is preparing to wrap things up.  For example, the host starts cleaning the table and loading the dishwasher, if he or she keeps glancing at the clock or watch every couple of seconds... look for cues like that.

5.  Bring a thoughtful gift. 

Well, this part is tough.  You have to know the host well to see what he or she likes.  Most people bring chocolates and wine to somebody's house party.  But personally, I hate both.  I can't wait to be invited to somebody's party and give those away.  You can ask the host ahead of time if you can bring a dessert instead of him or her making one. Then, you can either make a cake or other dessert, or buy a nice one. Ask the host if he or she, or other guests have allergies.  You want everyone to be able to enjoy your dessert.