Dear Ben,
There is no doubt about it, arguing in front of other people is uncomfortable for everyone involved. And yes, in some cases where their problems are bad enough that they will break social conventions, it can mean that a couple has given up on relationship, but that doesn't sound like you. At some point almost every couple, even the politest, may have cross words in front of others, and it doesn't spell the end of a relationship at all! It's healthy to disagree, it's just how you do it and how you resolve your differences that count!
Often when couples spend a lot of time with each other or are under pressure from a life changing event like a job change, house move, having a baby or dealing with a crisis, they can forget how to relax. This spills over into social occasions. Learning to park your troubles before you go out would be helpful.
If she is saying you are sarcastic and bossy, stand back a bit. Don't try and run the social situation for her, let her decide what she wants to do without jumping in and making decisions for the both of you. When she talks, listen to her rather than cutting her down or making a joke out of what she is saying. You might be doing this because you are nervous about making a good impression or being likable to others.
If she is feeling on edge give her plenty of time to leave the house, don't rush her and be a lot more chilled out about her anxiety. If you relax your whole attitude, she will slowly relax hers. It's only your attitude you can change, not hers, but hopefully she'll respond to you.
Have a quick 'breather' before you meet your friends to connect with each other. Sometimes it's stressful getting ready and traveling to a place. Before you go into a restaurant take a second to have a quick hug and tell each other you are going to have fun. Sometimes a simple affirmation like this can trick your brain into getting you in the right mood to be social, and allow you to leave the tension at the door.
Instead of taking your problems outside, get some outside help! It can be useful to talk things through with a professional relationship therapist who can give you some perspective on your issues.
www.marriageandfamily.ca