unfortunately there will always be bad customers like that. that it got that bad, and that it ended so poorly, is not always a necessary outcome of such a situation. your manager is a bad manager.

Your shop probably could have handled it better; politely telling him he's just like eight out of ten customers is dumb... you should have said "we do good work that takes time and we finish customers bikes on time... we don't make others wait because someone else thinks they're more important. if you want that, go find a shop with a lot of unfinished bikes around and throw money at the mechanic until they compromise their integrity."

really when it comes down to it, your manager sucks. the manager is there to make sure those situations don't get to that point and don't end like that.

and even if your manager doesn't suck... because honestly i don't know how it went and your manager may not have had any chance to intervene... striknein's right ... can't please everyone. that kind of interaction is part of retail.