As mothers, our protective instincts regarding our children make us unique. Reading your post, I didn't have the same instinct as you regarding the Nurse Practitioner, but it is likely the difference between reading it and living the experience with your own child.
Her bedside manner may have been lacking, but ultimately, her concern is for your son, and there may have been a small window of opportunity to vaccinate before tetanus is a real threat. Unfortunately, ER physicians are required to know a lot about many different things. If it wasn't a pediatric ER, they may not have been as aware of pediatric guidelines as the NP working in the field and may not have felt comfortable not knowing his immunization status.
All the way around, it sounds like communication was an issue from the Pediatric Urgent Care (which should have been able to suture and administer the tetanus vaccination) to the NP who clearly didn't take into consideration the hoops you'd already jumped through.
The office/practice manager is there to address such concerns. I might give it a few days to let emotions settle before filing an official complaint. The US is in a critical shortage of Primary Care providers. They're way overworked and making on average 25% less than they were 5 years ago. It doesn't excuse her bedside manner, it may just explain why she was lacking in the graces you needed at that point in time.
Most of my career has been spent in and out of doctor's offices. There are great doctors and mediocre doctors. Great NPs and those that don't really impress me. My OB/GYN missed a suspiciously swollen lymph node on my collar bone dismissing it as "not that exciting" whereas my FP (who I have been very critical about in the past) order the tests that led to my cancer diagnosis after my daughter's birth 2 years ago. Sometimes, we just catch them on the right days, and sometimes we don't. Medicine is stil as much an art as it is a science, and the ability to communicate with patients is a big part of that art. I truly wish you'd had a different experience.
Here's what the American Academy of Pediatrics says about tetanus vaccinations:
http://www.healthychildren.org/english/search/pages/resul...
Good luck. I hope your son is well and this experience is a distant memory soon.