As Neocon, Carpetbagger, and others have suggested, this was probably a classic situation for the use of O.C., because when this dude pushed the proximity envelope, his behavior merited a non-lethal response. I doubt you'd have gotten any legal repercussions from hosing him (except in the most liberal jurisdictions). Besides, it sounds like if you DID spray him, you could have just walked away.
There was another HR thread a week or 2 ago about O.C., and I posted several cases where I used O.C. (effectively) and tear gas (ineffectively). My experience has been -- when you walk the streets of ANY city at night -- sooner or later (at least about every 2-3 years) some pre-assault situations will cross your path. Most can be diffused via awareness and judicious use of O.C. I like my Surefire flashlights, but I'd go for the O.C. first, every time. A cell phone? With most urban police response times running 10-15 minutes? you'll be a s**t stain on the sidewalk by the time they arrive.
Frankly, unless there are witnesses abounding, I see no reason to stick around after dropping some street punk(s) with O.C. -- and then dealing with cops, the punk(s) 's lawyers, and wasting your own hard-earned money on your own legal defense team... money that'll buy more ammo and a nice gun collection. This strategy works best if your looks/dress is Vanilla Anonymous, so they can't readily I.D. you later. As guru John Farnam says, it pays to fly below the radar.
Overall, you did pretty good here, and we can all learn from this one.