EMMMMMM!
The staff party
You cope well enough with them day to day and you also cope with my sense of humour so I'm sure you can cope with them for a couple of hours. Pompoms and all

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Strategies
1. Set a length of time you will stay. If there is a meal then staying for one hour after the meal is fine.
No meal, 90 mins or after the first person leaves, which ever is sooner. Prepare the ground If you can't make the time you have set yourself. As soon as you arrive say you can't stay long because whatever or are waiting for a text that means you will have to leave because whatever. Everyone there will know that it isn't pleasant for anyone to be sober around a bunch of drunk people so making an excuse and leaving if they all get drunk is fine. I do it when I'm not drinking.
2. Try on the mindset that they are guests in your home, smile and humour them if you don't want to snap at them.
3. Most people love talking about themselves. Arrive armed with a batch of questions. How did you come to be doing this job? What were you doing before? What would you like to do? Married? Kids? Been on holiday lately? Where? What was it like? Favourite film? Etc. Show genuine interest in the answers and ask follow up questions. With any luck you won't have to talk about yourself if you don't want to. If all else fails, pull out your phone. Send me an email about it all if you like.
4. As Maisi said, most people tend to be better company one on one.
5. As far as questions about you go. You could try answering honestly where appropriate.
Questions about your religion? If, for example it fills you with warmth, joy and a sense of purpose and place then why not say so. Communicate how your faith makes you feel. It is certainly nothing to be ashamed of or something weird. Tell them about your recent trip to Bosnia or India. Communicate your love and joy.
6. Nowt wrong with telling people if they have gone too far with the sexist / racist / whatever jokes. You don't have to make a big thing of it just say something like, 'come on, that's taking it too far.' You are entitled to express your beliefs and act in accordance with your ethics. So long as you are measured and proportionate in your response, that will be fine.
7. If you imagine it is going to go terribly it probably will. Are there any other potential results?
The Job
Check in with yourself. What exactly is it that is bringing you down. Is it something you can change?
Is it the job or is it the job plus other stresses?
Is it something external or is it your response? If you feel it is compromising your ethics and grinding you down then maybe consider something else. As I recall, this job was a stepping stone rather than a home.
Anyhoo. That's my tuppence on the subject. Good luck with the party and let me know how it goes.
xxx