Regarding the bystanders 'just watching because they're scared.'
I would of just watched to. Not because I was scared, but because I watched that guy inviting it. I'm a big fan of people minding their own business. Seems to me that that guy wanted to fight. Who am I to impose my values (breaking up the fight he wanted)?
Regarding 'looking down' at the cell phone.
No doubt, he shouldn't of done it. However, recheck the film with this in mind. The motions were a part of the "tough-guy" routine. His gestures were saying,"alright, now I'm going to set this down and take care of you."
Regarding 'I don't know any Aikido that would of been handy here.'
Haven't you been practicing your side strikes as uke? Duck and side-strike the back of the head. He was vulnerable when he followed through on the punch.
What about your step-in thrusts? Haven't you noticed that it's a palm-heel strike to the chin? When he rears back to strike, he was susceptible.
Aikido's a study in balance, with that in mine, we have a few more rudimentary options: If fatty's left foot was forward, when his weight was forward through the swing, you could duck, slide between his right side and the on-lookers, grab his leg (which being all his weights on the front foot, should be pretty easy to lift), let him fall on his face, walk out while slapping his g.f. for the trouble
If his right foot is forward, duck, grab his leg and make him fall back as he's recovering his balance from all of it moving forward. Then slide out to your right, slapping the g.f. for the trouble on the way out
I once used the step-in thrust/palm heel like that. It works.