How can I help my husband control himself in awkward situations?

I have a question about my husband. First of all, he's a great man. He treats me very nicely and is very supportive. Those that know him well have a lot of respect for him. The only problem is that sometimes when he is in an awkward situation or doesn't know people very well, he can get very uptight and short tempered. He NEVER is physical- it's not like that, but he can be very abrasive, obnoxious and just rude sometimes. Others. when I know he feels comfortable, he is relaxed, calm and very pleasant. This is very embarring to me. My family hasn't gotten to know him very well because of this and I just cringe every time I know we will all be around each other. We currently live on the other side of the country from them, but my parents plan on visiting in the summer. I just want for him to be relaxed and enjoy himself, and for my parents to see what I see in him. My question is-how can I get him to relax in awkward situations or when he doesn't know people very well? How can I get him to control his temper in situations like that? Like I said, he's not like that all the time. He has a lot of good friends, ones that he's had for years. I don't want to make him sound like a monster..just looking for help.