Option A) Don't eat or perform your ablutions before the party. Arrive late, eat slowly and perform your ablutions. Spend about 5 to 10 minutes in the kitchen between activities, or wander from place to place like you have a purpose. This way you only need to nod or say “Hi” to people as you pass. When you've got nothing else to do, explain that you have to get up early the next day and leave early.
Option B) Eat well and perform all your ablutions before you go. Arrive early, before most people. Select the quietest, most isolated spot in the place, and set yourself up. Sit there and get into your head with something interesting. If anyone looks at you just act like you're tried, drunk or similar. When everyone else has gone, casually walk out thanking the host on the way.
Option C) Put a peg on your nose and ring up a few hours before the party. Express your sorrow and disappointment, but you've come down ill and can't make it. Then spend the time doing something interesting and more meaningful.
Option D) Go to the party when you like, Leave when you like. Take breaks by going into a quite room or a wander outside when you feel overwhelmed. If you don't know what to say to someone, just smile and nod. Talk about what you want to talk about. If people respond well, good. If people don't respond well, good. If you really don't enjoy it, next time select A, B or C.
Really, if you want to get your mind off your sorrows at home, you could go to a movie, museum, library or a coffee with friend or family. Rather than an activity akin to stabbing yourself in the eye with an ice pick.