It took me a short while to cognitively understand and behave like Easeful said. It took many more years to feel it in my heart. And there are still some behaviors which make me cringe (at least now it's just cringing and not wanting to crawl under the table).
I do relate to how the evening went. I've found over the years that if I "prepare" my friends for what they might witness, I don't feel embarassed, I feel supported. Perhaps if you're in a similar situation again, it might help to call the secondary parties (in this case your friend) and gently let them know that "dad doesn't operate on all cylinders, and his behavior can be a bit nutty most of the time - just wanted to prepare you before it started happening so you can be ready". If they ask for examples, give them. Then, when dad acts nutty, it's really more of a confirmation - at least for me - it feels more like "see? It really isn't me. He really is a nutjob. He really is tragically embarassing"
This helps get it "out of the closet" and into fresh air before the event, so that when the inevitable happens, not only do you have nothing to feel guilty about (we can't pick our parents afterall), but you also will usually recieve affirmation from your friend/poor other person involved when they come back to you and say something like "man, I knew you said your dad was dotty, but boy - that was way more than I expected! You were right!"
It seems to work well for me. I get affirmed, the other person has a chance to mentally prepare for odd behavior, and I don't have to be embarassed because I can catch their eye with an "told ya!" look and they smile.
I know I was pretty well brainwashed into "don't air your dirty laundry". But I found when I started airing it, *I* felt much better because guess what? It's not mine. It's somebody else's and it was stinking up my life. So I air it in advance, and it cuts way down on the stress. After all, it's not like the other people aren't going to notice something's going on.