I always think that people who propose in public are asking for humiliation!
My husband was 100% sure that I would say yes, and he was STILL nervous. I thought he was going to propose to me at one point (he kept dropping hints, I thought) and we had a screaming match after it didn't happen. He said, "I'm going to ask you this year, but I won't tell you when. I want to make this a surprise."
He was THAT sure that I was going to say yes and he decided NOT to do it in public. He was also so nervous that I was THIS CLOSE to picking a fight because he was behaving so distantly that day and he kept leaving the restaurant to answer phone calls (of course, everyone was calling to ask him if he had proposed already).
When my uncle proposed to my aunt, I actually hid behind the couch when he proposed. There's something so scary about the possibility of rejection, never mind when an audience is watching!
ETA: Dude is an idiot. He should have said yes and told her in private to spare her! It wasn't like he didn't love her or want to marry her. Stoopid!